Thanks Carlos for the image!

The official story of what happened on 9/11 never fails to shock. Four American airliners are hijacked by Osama Bin Laden's terrorists in an attack on the heart of the Western world on September 11, 2001.

Two are deliberately flown into New York's famous Twin Towers, which collapse. A third rams into the United States defence headquarters at the Pentagon, in Washington D.C.

The last goes down in rural Pennsylvania, 150 miles north of the capital, after a tussle between the hijackers and some of the passengers onboard, whose bravery was recently portrayed in a Hollywood film, United 93.

Nearly 3,000 ordinary, decent Americans die in the attacks, provoking the U.S. President George W. Bush to mount a global war on terror, which leads to the invasion of Iraq, with Britain in tow.

Or that's how the official story goes.

Yet today, more than five years on, this accepted version of what happened on 9/11 is being challenged by a 90-minute internet movie made for £1,500 on a cheap laptop by three young American men. The film is so popular that up to 100 million viewers have watched what is being dubbed the first internet blockbuster.

The movie was shown on television to 50 million people in 12 countries on the fifth anniversary of 9/11 last autumn. More than 100,000 DVDs have been sold and another 50,000 have been given away. In Britain, 491,000 people have clicked on to Google Video to watch it on their computers.

Called Loose Change, the film is a blitz of statistics, photographs pinched from the web, eyewitness accounts and expert testimony, all set to hip-hop music. And it is dramatically changing the way people think about 9/11.

A recent poll by the respected New York Times revealed that three out of four Americans now suspect the U.S. government of not telling the truth about 9/11. This proportion has shot up from a year ago, when half the population said they did not believe the official story of an Al Qaeda attack.

The video claims the Bush administration was, at the very least, criminally negligent in allowing the terrorist attacks to take place. It also makes the startling claim that the U.S. government might have been directly responsible for 9/11 and is now orchestrating a cover-up.

Unsurprisingly, the film's allegations have been denied, even roundly condemned, by White House sources and U.S. intelligence services.

Only this week, the letters page of the Guardian newspaper was full of discourse about Loose Change, which was made by a trio of twentysomethings, including a failed film school student and a disillusioned ex-soldier.

Indeed, the movie's assertions are being explored by a number of commentators in America and Britain - including the former Labour Cabinet Minister Michael Meacher - who are questioning the official account of 9/11.

Mr Meacher, who last year proposed holding a screening of Loose Change at the House of Commons (he later changed his mind), has said of 9/11: "Never in modern history has an event of such cataclysmic significance been shrouded in such mystery. Some of the key facts remain unexplained on any plausible basis."

These words were written in a foreword for Professor David Ray Griffin's bestselling book, The New Pearl Harbour (a pointed reference to the conspiracy theory that President Roosevelt allowed the Japanese to assault the U.S. fleet in 1941, in order to force America into World War II).

Griffin, now nearing retirement, is emeritus professor at the Claremont School of Theology in California and a respected philosopher. While Loose Change is capturing the interest of internet devotees, Professor Griffin's equally contentious theories are receiving standing ovations in book clubs across the U.S.

Together, the book and the movie have raised the question: could the attack be a carbon copy of Operation Northwoods, an aborted plan by President Kennedy to stage terror attacks in America and blame them on Communist Cuba as a pretext for a U.S. invasion to overthrow Fidel Castro?

In other words, on a fateful September morning in 2001, did America fabricate an outrage against civilians to fool the world and provide a pretext for war on Al Qaeda and Iraq?

This, and other deeply disturbing questions, are now being furiously debated on both sides of the Atlantic.

Why were no military aircraft scrambled in time to head off the attacks? Was the collapse of the Twin Towers caused by a careful use of explosives? How could a rookie pilot - as one of the terrorists was - fly a Boeing 757 aircraft so precisely into the Pentagon? And who made millions of dollars by accurately betting that shares in United and American Airlines, owners of the four doomed aircraft, were going to fall on 9/11 as they duly did?

An extremely high volume of bets on the price of shares dropping were placed on these two airline companies, and only these two. In the three days prior to the catastrophe, trade in their shares went up 1,200 per cent.

Initially, like most people in America, Professor Griffin dismissed claims the attacks could have been an inside job.

It was only a year later, when he was writing a special chapter on American imperialism and 9/11 for his latest academic tome, that the professor was sent a 'timeline' on the day's events based entirely on newspaper and television accounts. It was then that he changed his mind.

And one of the most puzzling anomalies that he studied was that none of the hijacked planes was intercepted by fighter jets, even though there was plenty of time to do so and it would have been standard emergency procedure in response to a suspected terrorist attack.

Indeed, it is mandatory procedure in the U.S. if there is any suspicion of an air hijack. In the nine months before 9/11, the procedure had been implemented 67 times in America.

Readers of The New Pearl Harbour and viewers of Loose Change are reminded that it was 7.59am when American Airlines Flight 11 left Boston. Fifteen minutes later, at 8.14am, radio contact between the pilot and air traffic control stopped suddenly, providing the first indication that the plane might have been hijacked.

Flight 11 should have been immediately intercepted by fighter pilots sent up from the nearby McGuire Air Force Base in New Jersey. They could have made the journey to the World Trade Centre in three minutes.

But, surprisingly, F-15 fighter jets were instead ordered out of an airbase 180 miles away at Cape Cod. They appear to have flown so slowly - at 700mph, instead of their top speed of 1,850mph - that they did not arrive in time to stop the second attack, on the South Tower of the World Trade Centre. They were 11 minutes too late.

And this is not the only worrying question. Incredibly, the attack on the Pentagon was not prevented either. The defence headquarters was hit by the hijacked American Airlines Flight 77 at 9.38am. But fighter jets from Andrews Air Force Base, just ten miles from Washington, weren't scrambled to intercept it.

Instead, jets were ordered from Langley Air Force Base in Virginia, 100 miles away. By the time they arrived, Flight 77 had already hit the Pentagon.

So what of the fall of the Twin Towers?

The official version is that the buildings collapsed because their steel columns were melted by the heat from the fuel fires of the two crashed planes.

It is a mantra that has been repeated in White House briefings, official inquiries into 9/11, leaks by the American intelligence services and almost every TV documentary on the attack in the U.S. and Britain.

But, according to the allegations of Loose Change (which are endorsed by Professor Griffin), the science does not stand up. Steel does not begin to melt until it reaches around 2,800 degrees Fahrenheit, but open fires of jet fuel - such as those in the Twin Towers inferno - cannot rise above 1,700 degrees.

Professor Griffin and the makers of Loose Change are convinced the Twin Towers were deliberately blown up.

The film shows clip after clip of the towers coming down in one fell swoop to loud and distinct booms. Were they the sound of detonators being set off?

And the Pentagon attack? The hotly disputed theory of the film and Professor Griffin is that a passenger plane never hit the building at all.

The terrorist pilot, Hani Hanjour, was so slow to learn the fundamentals at flight school that his tutors reported him to the authorities for his incompetence five times.

How could he have guided the huge aircraft in such a complex manoeuvre into the building? And if he did, what happened to the aircraft?

The Loose Change narrator says: "The official explanation is that the intense heat from the jet fuel vapourised the entire plane. Indeed, from the pictures, it seems there was no discernible trace of a fully loaded Boeing 757 at the crash scene.

"But if the fire was hot enough to incinerate a jumbo jet, then how could investigators identify 184 out of 189 dead people found at the defence headquarters?"

Intriguingly, the narrator adds: "The only visible damage to the outer wall of the Pentagon is a single hole no more than 16ft in diameter. But a Boeing 757 is 155ft long, 44ft high, has a 124ft wingspan and weighs almost 100 tons.

"Are we supposed to believe that it disappeared into this hole without leaving any wreckage on the outside? Why is there no damage from the wings or the vertical stabiliser or the engines which would have slammed into the building?

"Remember how big the engines were," the film adds persuasively.

"If six tons of steel and titanium banged into the Pentagon at 530mph, they would bury themselves inside the building, leaving two very distinct imprints. And yet the only damage to the outer wall is this single hole."

And what of the Boeing's 40ft high tail? "Did it obligingly duck before entering the building?" asks Professor Griffin.

So if a commercial aircraft did not hit the building, what did? The wildest of all the theories in Professor Griffin's writings - echoed in Loose Change - is that the Pentagon was attacked by a military missile of some kind. Certainly, several onlookers quoted in the film claim that they saw a tiny aircraft piercing the defence HQ.

Another witness says it made a shrill noise, quite unlike a giant passenger plane.

So if it wasn't hijacked and flown by a terrorist into the Pentagon, what happened to Flight 77, last heard of on its way to Ohio?

No one knows. But one thing is sure, asserts Professor Griffin. Dick Cheney, the U.S. vice- President, and Condoleezza Rice, at the time President Bush's national security adviser, were in the White House bunker as the drama unfolded.

They, and their advisers, knew a hijacked aircraft was heading towards Washington. The obvious target was the White House, not the Pentagon. Yet Cheney and Rice were never evacuated from the White House. Did someone in high places already know that they were safe and that it was the Pentagon that was going to be the target?

Of course, no account of 9/11 by the conspiracy lobby is complete without a minute-by-minute observation of President Bush's behaviour.

He was hundreds of miles away in Florida, about to read a book to primary school children when the worst terrorist attack of the modern age happened.

The President reportedly showed little reaction when an aide told him that the first plane had crashed into the Twin Towers. Why not?

He, apparently, told the school's principal: "A commercial plane has hit the World Trade Centre, but we're going ahead with the reading thing anyway."

Then President Bush, who is also the commander-in-chief of the American military, settled down to recite My Pet Goat to a group of seven-year-olds.

He was interrupted a few minutes later by a whispered message in his ear from an aide that a second aircraft had hit the Twin Towers.

The President's face, captured by photographers at the school, remained completely passive. He showed no sign of emotion.

Now it must have been obvious a terrorist maelstrom was being unleashed on his country. But three days later, back in the American capital, he was a different man. By now he was certain that Osama Bin Laden and his Al Qaeda henchmen were to blame.

Surrounded by the Christian evangelist preacher Billy Graham, a cardinal, a rabbi and an imam, the President delivered a sermon in America's national cathedral in Washington.

The words he uttered are recounted by both Professor Griffin and the makers of Loose Change.

President Bush announced: "Our responsibility to history is already clear: to answer these attacks waged against us by stealth, deceit and murder and rid the world of evil."

The scene had been swiftly set for the West's war on terror.