The plot by America’s military bosses was devilish in both design and intent – to fabricate an outrage against innocent civilians, fool the world and provide a pretext for war. In the pentagon, a top secret team drew up a plan to simultaneously send up two airliners painted and numbered exactly the same, one from a civil airport in America, the other from a secret military airbase nearby.

The one from the airport would have military personnel on board who had checked in as ordinary passengers under false names. The one from the airbase would be an empty drone, a remote-controlled unmanned aircraft.

Somewhere along their joint flight paths, the passenger-carrying plane would drop below radar height, and disappear, landing back at the airbase and unloading its occupants in secret.

Meanwhile, the drone would have taken up the other plane’s designated course. High over the island of Cuba, it would be exploded in mid-air after broadcasting an international distress call that it was under attack from enemy fighters.

The world would be told that a plane load of blameless American holidaymakers had been deliberately shot down by Fidel Castro’s Communists – and that the US had no choice but to declare war and topple his regime.

This ‘agent provocateur’ plan – code named OPERATION NORTHWOODS and revealed in official archives – dates from 1962 when the Cold War was at its height. (Bulldog Manifesto adds: See Operation Northwoods here and here)

Four decades later, there are a growing number of people who look back at this proto-conspiracy and then to the events of 9/11 and see uncanny and frightening modern parallels.

For Cuba, read Iraq, say these skeptics. For the dummy airliner, read the Twin Towers in New York.

The Northwoods plan is crucial to the argument presented in a hugely provocative – many would say fantastical – yet, at times, genuinely disturbing new analysis of 9/11 by two radical British based journalists, Ian Henshall and Rowland Morgan.

Did the CIA actively help the hijackers?

In it, they examine various conspiracy theories that suggest the Bush administration connived in the devastating aerial attacks on New York and Washington four years ago.

The reason? To give Bush the excuse he wanted to push ahead with his secret, long-held plane to invade Iraq and capture its oilfields.

As we shall see. Many of the theories they raise are outlandish in the extreme. It would be easy to dismiss them as hokum, the invention of over-active imaginations among those whose instinct is always to find some way to blame America for the world’s ills.

Are we really supposed to believe that the CIA actively helped the hijackers succeed – or even that the US government staged the whole attack and itself murdered thousands of its own citizens?

Some would say that even in discussing suck notions, we are lending comfort to terrorists and doing a disservice to the dead.

However, much of evidence the authors present is undeniably compelling – and their arguments sound rather less preposterous in the light of OPERATION NORTHWOODS all those years ago. That plan was proposed in all seriousness by America’s Joint Chiefs of Staff in a memo to the Secretary of Defence. It got as far as the Attorney General – Robert Kennedy, brother of the president, John Kennedy, before being vetoed.

It is proof, says Henshall and Morgan, that forces at the top of the US Government are capable of conceiving a deadly, devious and fraudulent plan to further their own secret ends – even under such a supposedly ‘nice guy’ president as JFK.

In which case, can the idea of a 9/11 plot by those who serve the deeply mistrusted Bush really be ruled out with total certainty, without at least considering the arguments?

Of course, the official explanation for 9/11 is that Al Qaeda just got lucky that sunny morning in September 2001.

The terrorists conducted their attacks without outside help, by this account, and intelligence and other blunders by the US authorities that contributed to their terrible success – for example, ignored warnings that an attack involving aeroplanes was likely, or issuing US entry visas to 19 Islamic fanatics set on murder – were just that: blunders.

This is the White House’s version and it was endorsed by a Washington commission of inquiry under Thomas Kean published last year.

But, according to Henshall and Morgan, the story is full of gaping holes and unanswered questions. And the most startling question, which remains unresolved, they say, is why the hijackers’ principal target, the two 110-storey towers at the World Trade Centre in New York crumbled so easily.

No-one who watched each building suddenly cascade into dust and debris in just 20 seconds will ever forget the slow-motion horror. But now the question is asked: was it all too pat, too neat?

Though 30 years old, the towers had expressly been built to survive the impact of a Boeing 707, a plane the same size and carrying as much fuel as the ones that struck. That they collapsed after being hit and fell at such speed was unprecedented in the history of architecture. It astonished many engineers.

The official explanation is known as the Pancake Effect – steel supports melting in the intense fireball, causing the floors to tumble down on each other.

The problem here is that the heat from the explosions was probably not nearly as great as people tend to assume.

There was indeed a lot of kerosene from the aircraft fuel tanks when flight 11 from Boston hit the North Tower between the 94th and the 98th floors but pictures show that most of this fireballed outwards. Experts have questioned whether the fire ever got hot enough to melt the buildings’ steel frames.

Oddly, too, original estimates by firefighters after the second plane, Flight 175, hit the South Tower, were that the blaze was containable.

Two firefighters actually reached the crash zone on the 78th floor and a tape exists of them radioing down that just two hoses would be enough to get the fire under control (The Bulldog Manifesto adds: Here is the tape. Its the firefighters describing the fire inside the building before it collapsed)– in which case the situation should have been little different from a ‘normal’ office fire, and no steel tower ever collapsed as the result of such a blaze.

‘The fire wasn’t hot enough to cause a collapse’

Kevin R Ryan, laboratory director at a US underwriting firm specializing in product safety, was sacked from his job last year after questioning the official explanation. (The Bulldog Manifesto adds: Here are a bunch of links regarding this fact.)

“The buildings should have easily withstood the thermal stress caused by the burning jet fuel”, he said. “If steel did soften or melt, this was certainly not due to jet fuel fires of any kind, let alone the briefly burning fires in those towers. That fact should be of great concern to all Americans.”

Intriguingly, Ryan claimed that his firm had checked and approved the steel used in the towers when they were built. This was later vehemently denied by the bosses who sacked him.

To add to the mystery, the tape of the two firemen was kept secret and when relatives were finally allowed to listen to it, they had to sign strict confidentiality agreements.

If the Pancake Effect theory is wrong, there’s one obvious alternative: that the towers were brought down by the sheer impact of the planes hitting them. But this, according to the skeptics, ignores basic physics. (The Bulldog Manifesto adds: Check this out.)

The initial hit on the North Tower, for example, destroyed 33 of the 59 columns in its north face. This meant the damage was asymmetrical, so any resulting collapse would surely have been lopsided.

In fact, the building fell evenly. The TV aerial on the summit sank vertically, in a straight line.

There were other strange anomalies. According to the Kean Commission, when the first plane struck: ‘A jet fuel fireball erupted and shot down a bank of elevators, bursting into numerous lower floors, including the lobby level, and the basement four storeys below ground.’

Unlikely, say Henshall and Morgan. A firm by a French documentary crew, who by chance were following a New York firefighting team that day, shows the first men arriving. The lobby was covered in fine debris and the windows were shattered but there was none of the soot or oily residue that burning jet fuel would have left behind.

Meanwhile down in the basement, a 50-ton hydraulic press was reduced to rubble and a steel and concrete fire door demolished. Witnesses there said the destruction was less like that from a fireball flash and more like that from a bomb.

Some firefighters told reporters that day that they thought there had been bombs in the building – before apparently being silenced by their chiefs. So had Al Qaeda cleverly placed explosives inside the rowers as well as attacking them from the air?

Or, as conspiracy theorists would have it, had some homegrown agency mined the towers to make sure they fell – but neatly without collapsing over the rest of Manhattan, America’s financial and business heartland?

The authors quote an expert demolition contractor from Pennsylvania, Michael Taylor, who said the fall of the buildings ‘looked like a controlled demolition’.

Another expert, Van Romero, vice-president for research at the New Mexico Institute of Mining and Technology, reached the same opinion after studying videos of the disaster, and concluded that ‘explosive devices inside the buildings’ caused them to collapse. (The Bulldog Manifesto adds: Here is a bio on Van Romero.)

Strangely and without explanation, he recanted that view just ten days after going public with it. Might he possibly have been leaned on?

Even stranger, say Henshall and Morgan, was the collapse of a third building on the World Trade Centre site, a smaller 47-storey block known as WTC7, which was largely ignored by the world’s media. (The Bulldog Manifesto adds: Check this out on WTC7. In my view, Building 7 is the easiest way of revealing the truth about 9/11. Building 7 is simple and easy to understand. More than that, it can't be denied!

It had not been hit by a plane yet it, too, mysteriously fell many hours after the Towers had gone.

The official explanation for this was that fuel stores caught fire as a result of debris from the burning towers, the building began to bulge in one corner, and after that it was unsalvageable.

But remember that, according to Henshall and Morgan, a steel-framed building had never collapsed as a result of a fire before this day. And, again according to the authors, WTC7 appears almost untouched by fire in photographs taken at the time.

The landlord of the World Trade Centre site, Larry Silverstein, explicitly suggested at one point that WTC7 was deliberately demolished. He told a US TV documentary that a decision was taken to ‘pull’ the building rather than risk loss of life, though this was later denied.

Certainly, according to Henshall and Morgan, the building’s fall in seven seconds was just as textbook-tidy and suspicious as the collapse of the Twin Towers. Given that it also housed offices of the US Secret Service, the CIA and the Defence Department, this has led conspiracy theorists to give it a key role in the supposed 9/11 plot – as we will see shortly.

Part of the whole problem, according to Henshall and Morgan, is that vital evidence about what happened was destroyed or muddied in the wake of the atrocity.

One expert said there were bombs inside the towers

Ground Zero, the base of the towers, was fiercely protected by the authorities – understandably so because it not only contained human remains but a cache of seized drugs held in an FBI office and more than $1 billion of gold from bank vaults in the Buildings.

Yet what went on behind all the heavy security?

After most air disasters, the wreckage of the planes is meticulously gathered up and pieced together in search of clues.

Extraordinarily, in the course of removing the rubble from the Twin Towers to a nearby landfill site, the 9/11 salvage operation seems to have ‘lost’ four six-ton aircraft engines, besides failing to find the ‘black box’ flight data recorders and cockpit voice recorders from either of the planes.

These data boxes – which could have revealed exactly what happened in the doomed jets – are deliberately designed to withstand heavy impacts and exceptionally high temperatures. It is, according to experts, very rare for them not to be recovered after an accident.

Unfortunately, according Henshall and Morgan, there was a singular lack of official zeal even to establish the very basic fact that the aircraft that hit the Twin Towers were the same as those that took off from Boston.

Perhaps, with almost the entire world watching the attacks on TV, it hardly seemed necessary to prove the glaringly obvious. But this failure to follow standard procedures for accident investigation once again gave encouragement to the conspiracy theorists.

And then there was the oddity of the single passport. The black boxes may have been destroyed and steel girders melted – yet somehow one of the hijackers’ passports avoided this inferno and was found intact in a nearby street by ‘a passer-by’. (The Bulldog Manifesto adds: Here is a good resource regarding the "miracle passport".)

To Henshall and Morgan, that seems absurd, as does the almost instant identification of this person as a hijacker rather than a passenger or a Twin Towers office worker. Conspiracy theorists suspect the passport was planted to help establish the official story in the first, critical hours after the disaster.

Why didn't fighter planes intercept the hijackers?

Still more unanswered questions surround what happened at the Pentagon in Washington, in the third successful terrorist attack that day.

After taking off from Dulles Airport, Washington, American Airlines Flight 77 dropped off the radar screens for 36 minutes when its transponders sending signals back to air traffic control were switched off.

When the blip reappeared, it was closing on the city but where precisely the aircraft had been for the past half an hour was a mystery. Nor could anyone in air traffic control figure out what it was.

Experienced officials apparently watched its speed and maneuverability and thought it must be a military plane. Conspiracy theorists maintain this is precisely what it was.

In a repeat of New York, no evidence has ever been produced from the wreckage to prove that it was Flight 77 that hurtled into the side of the Pentagon at 350mph.

Photographs show that the hole it made was large enough for the fuselage of a Boeing 757 but not for the wings and the tail, though these supposedly disappeared through the gap and then vapourised.

For the conspiracy theorists, this points to a conclusion that what hit was not Flight 77, and not even a jetliner.

Some witnesses claim the plane they say hit the Pentagon was a small one, an eight – or 12-seater, and that it did not have the roar of an airliner but the shrill whine of a fighter plane, One witness is convinced it was a missile.

The authors say the matter could be cleared up by CCTV footage of the crash from a nearby filling station, a hotel and traffic surveillance cameras. Unfortunately, the FBI seized all three videos within minutes of the crash and they have never been released.

In essence, to the extreme conspiracy theorists, what took place on 9/11 was a repeat of the aborted OPERATION NORTHWOODS.

Far from being an attack by Islamic terrorists, they say, the events were a complete hoax, a conjuring trick by the US government in just the same way that Kennedy’s generals wanted to fool the world over Cuba.

Planes were swapped, ‘drones’ slammed into the World Trade Centre (which was mined with explosives as well) and the Pentagon, and the identities of alleged hijackers from the Middle East were stolen or invented to put the blame on Al Qaeda. (The Bulldog Manifesto does not subscribe to the remote contol theory. Its pure speculation at this point to assume that.)

Along with the ‘passengers’ who apparently boarded the planes, the ‘suicide hijackers’ are now either dead or living under different identities, just as the pentagon planned fro the military personnel it was going to use back in 1962. (The Bulldog Manifesto adds: See this BBC article) )

The theory seizes on the fact that, like the plane that apparently hit the Pentagon, both Flight 11 and Flight 175 switched off their transponders on their way to the Twin Towers and disappeared from Radar screens. According to the skeptics, this gave them time and opportunity to land at the handily located Griffiss Air Force Base, a Pentagon command center which also houses research laboratories into advanced computers and radar. There, they were supposedly replaced by remote-controlled substitutes.

In technical terms, this is not as far fetched as it sounds. The US military experimented with unmanned aircraft as far back as World War II and there have been successful jet models since. Well-connected conspirators, so the theory goes, would have little difficulty getting their hands on a system to fit in an airliner. (The Bulldog Manifesto adds: Once again, I don't subscribe to the 'drones' theory. There aren't any real facts there..)

The switch would supposedly be foolproof because, as we have seen, the aircraft in the ruins would not be properly identified.

Then there was the smaller building known as WTC7. It was the obvious point from which to run the New York end of the scam, guiding the planes into their target. Afterwards, of course, the evidence had to be destroyed, hence its demolition.

Taken as a rush, and without looking at the detail this might seem vaguely plausible. But could we really have been so totally and utterly conned?

Common sense says no. An operation of such intricacy and complexity would require the co-operation – and the silence until death – of thousands of people. Everything we have read about the victims on the planes, and their heartbroken relatives, would be a carefully constructed sham.

It might just be possible in a totalitarian society but surely not in a flawed yet robust democracy like America. And with four missions (the hijackers of the fourth plane, Flight 93, were overthrown by its passengers), not just one as in OPERATION NORTHWOODS? No.

To be fair to Henshall and Morgan, they make it clear that they themselves are not advocating such an extreme theory of empty planes and hoax attacks.

They admit the Pentagon’s radar reconstructions suggest the planes were not switched, and that alleged Al Qaeda ringleaders are said by their interrogators to have confirmed the official account.

Instead of retreating into fantasy, they simply insist that something is being held back – that we have not been told the full story. And it’s hard to discount all their arguments.

Why, they ask, were air traffic controllers so slow to report suspected hijackings to the military that day in breach of standard procedures, with the result that fighter planes arrived too late to intercept?

Flight controllers in four separate incidents were unaccountably slow to realize that something was wrong and alert the military authorities. Even after one plane was definitely known to have been hijacked, they failed to respond promptly when others went missing. The air force scrambled from the wrong base.

For some reason, too, when fighter planes eventually were scrambled to New York, they were from an airbase 150 miles away, rather than the much closer one in New Jersey. The Twin Towers were ablaze before they got there.

All the while the local TV channels were smoothly getting eye-in-the-sky helicopters into the air over the World Trade Centre. In the words of the authors: “Their routine mobilizations stand in stark contrast to the apparent impotence and indecisiveness of the $350-billion-a-year US military.

Yet for all the shortcomings of the Federal Aviation Authority and the US Air Force that day, no-one was ever fired or reprimanded.

One explanation for this paralysis is that there was, as fate would have it, an air defence exercise going on in US airspace that same day, codenamed Vigilant Guardian. The air traffic controllers were confused by this, thinking the planes disappearing from their screens might be part of the exercise.

Coincidence? No say the 9/11 sceptics. This was exactly the sort of smokescreen operation that anyone wanting to make life easier for the hijackers would launch to paralyse any authorities that might get in the way.

When the first evidence came that hijackings were taking place, traffic control officials wasted valuable time wondering whether or not this was part of the Vigilant Guardian exercise.

Suck a smokescreen fits well with two types of government-inspired plot postulated by 9/11 sceptics – popularly known as ‘LIHOP’ and ‘MIHOP’.

‘LIHOP’ – ‘Let It Happen On Purpose’ – holds that since the turn of the new century, radical right-wingers in Washington (the so-called new-cons) had been keen to get a US military presence in the Middle East oilfields and were also desperate to do something about Al Qaeda, which had been targeting US interests overseas.

When evidence came in of an impending terrorist attack, they decided to ignore it. They intended that it should succeed. It would act at the very least as a ‘wake-up’ call to their apathetic fellow countrymen and at best as an excuse for war.

In the much the same way, some historians believe, President Roosevelt knew in advance from broken codes about the Japanese attack on Pearl Harbour in 1941 – but let it happen, at the cost of 2,400 lives, because he wanted an excuse to join World War II.

‘MIHOP” takes a step on from this – ‘Make it Happen On Purpose’. This theory has the same motivation but the active involvement of US agents. Planted in Al Qaeda, they helped organize the plot, or at the very least cleared a path for the hijackers.

These agents may even have tried to keep down casualty figures, which some think were suspiciously small in the circumstances.

The plane that hit the Pentagon was seen to swerve at the last minute and hit an area of the building that was largely unoccupied – and which had just been fitted with reinforced external walls and blast-resistant windows. A crash into the other side would have killed and maimed many thousands instead of just 125.

In New York, too, more than 50,000 inhabitants of the Towers were targeted but just 2,600 killed – not least because of the orderly way in which the buildings collapsed, after most of the occupants had been evacuated. Was this an example of a ‘managed’ atrocity?

For most observers, the idea of US involvement in the attacks still strains credulity beyond breaking point. Yet that catalogue of unanswered questions remains troubling.

Some are very basic. How, for example, did the hijackers manage to slip past airport security with weapons?

The White House explanation is plastic knives, but there has never been any independent confirmation of how the men were armed. Some passengers who made phone calls from the doomed planes said they witnessed stabbings but others spoke of bombs and even guns being used.

To some, the official recourse to ‘plastic knives’ smacks of a cover-up to conceal security lapses – or worse, a deliberate turning of blind eyes.

Doubts are even raised over the gung-ho story of Flight 93, the fourth plane in the attacks, which passengers apparently seized back from the hijackers, causing it to crash into a field but miss Washington.

The legend of the heroic cockpit-storming, launched to cries of ‘Let’s Roll’, was a product of tapes that have never been authenticated or released to anyone other than the victims’ relatives, who were sworn to secrecy.

Henshall and Morgan say the matter could be cleared up if recordings or billing evidence from phone companies were produced but they never have been.

This call for transparency is the thrust of their whole argument. It is time, they say, for a full and truly independent inquiry into 9/11 that will reveal all the facts and silence the rumours.

One thing it could consider would be the anthrax attack on America three weeks after 9/11. Five recipients of contaminated letters died, postal facilities were closed, as were office buildings on Capitol Hill where hundreds of lawmakers and staff were tested and given an antibiotic.

At the time, this was seized on by the Washington power-brokers pressing for action against Iraq. ‘Who but Saddam Hussein could have supplied Arab terrorists with anthrax,’ they asked.

By contrast, skeptics about 9/11 see this as this finishing touch to the grand plot – an attempt to distract attention from any doubts about the atrocities and the lessons to be learned from them.

They may have a case. The letters mysteriously stopped and the anthrax spores were identified by scientists as a particular strain stemming only from the government’s own labs in Maryland.

But by then the scare had shut down congress at a crucial time, when questions about 9/11 were beginning to surface, and helped deepen the mood of fear and paranoia among ordinary Americans.

It was those fears, say the skeptics, that Bush exploited to get his way on Iraq. Had he plotted it that way all along? Henshall and Morgan raise enough awkward points to make it a thought that cannot simply be laughed out of court.

After all, Bush and Blair, took us to war assuring us that ‘the Iraq regime continues to possess some of the most lethal weapons ever devised’. Yet those weapons of mass destruction have not been found and many doubt they existed.

With public trust one of the major casualties of the war, can any of us be absolutely sure we have not been caught up in a lie and perhaps a bigger one even than we ever though possible?

In their inquiries Henshall and Morgan may have discover no smoking guns – but they have certainly left a whiff of something sinister in the air.