Next Monday afternoon, Matt Campbell will stand outside BBC Broadcasting House in London’s Portland Place, protesting about the killing of his brother, Geoff, and 66 other Britons, in the 9/11 terror attack at the New York World Trade Centre.

After the horror on September 11, 2001, there was no trace of Geoff. The 31-year-old risk analyst had been attending a conference on the 106th floor in the North Tower, a short stroll from the Manhattan apartment where he lived with his American fiancée, Caroline.

At first, his family clung to the hope he was alive, until one year later fragments of a shoulder blade bearing Geoff’s DNA were found among Trade Centre rubble at a landfill site.

Matt began asking questions. He has not stopped since. He, and others who will be at the BBC protest, refuse to accept the official story about 9/11: that four U.S. airliners were hijacked by Islamist terror chief Osama Bin Laden’s pilots. Two were flown into New York’s famous Twin Towers, which collapsed.

Doubts continue to be cast on the official explanation for the 9/11 terror attacks in New York (pictured)

A third rammed into the U.S. Defence Headquarters at the Pentagon in Washington DC. The last went down in rural Pennsylvania, 150 miles north of the capital, after a tussle between the hijackers and passengers, later portrayed in the Hollywood film United 93.

Seven hours later, a third tower at the World Trade Centre, WTC7, fell to the ground over seven seconds, even though no plane had hit it.

The red building, 100 yards from the 110-storey Twin Towers, was less than half their height at just 47 floors, and few people even know of its existence. It had already been evacuated after the planes had hit the main towers.

In total, 2,977 people died, provoking President Bush to mount the ‘War On Terror’ that led to the invasion of Iraq, with the UK in tow.

Yet as Monday’s anniversary approaches, Matt, a former City worker who is married with three children and lives in Sussex, insists that 9/11 did not happen in the way we have been told and that there has been a huge official cover-up to disguise the truth.

‘There are so many questions that the Americans and the British Establishment refuse to answer,’ he says. ‘I believe that my brother and thousands of others were murdered on 9/11 and there has been a cover-up. We, as a family, are still overcoming this tragedy, but we will never stop seeking the truth.’

He is not alone in his quest. A survey in U.S. magazine Live Science last year revealed that most Americans (53 per cent) believe the U.S. Government has concealed — and continues to conceal — vital information about the 9/11 attacks. Crucially, a team of engineers at the University of Alaska concluded this week, after two years of forensic research, that fire could not have caused the collapse of WTC7.

Indeed, though the official story is that WTC7 was weakened by fires caused by debris from the attack, it’s the only steel skyscraper in the world ever to collapse purely as a result of a blaze.

Geoff Campbell (pictured with fiancee Caroline Burbank) was one of 67 Britons killed in the attack. His brother Matt refuses to believe the official 9/11 explanation

And a new book by an academic who has become an authority on 9/11, Professor David Ray Griffin, says that to believe that this building fell to the ground without explosives being involved is asking the public to believe in ‘miracles’.

Griffin, a retired philosopher at Claremont School of Theology in California, adds in his bestseller Bush And Cheney: How They Ruined America And The World, about the ex-president and his vice-president Dick Cheney: ‘There is a growing consensus that 9/11 allowed the U.S. to adopt extreme, unwarranted policies. They include the War On Terror and the attacks on Afghanistan and Iraq as first steps in taking control of the Middle East.’

He, and other 9/11 sceptics such as Matt, have asked if the attack was, in fact, a copy of Operation Northwoods, an aborted plan during John F. Kennedy’s presidency to stage terror attacks in America and blame them on Communist Cuba as a pretext for a U.S. invasion to overthrow dictator Fidel Castro.

In other words, on that September morning in 2001, did the White House fail to stop — or even fabricate — an outrage against its own civilians so as to provide a pretext for war on Al Qaeda and Osama Bin Laden?

Although there have been countless conspiracy theories about 9/11, the idea that the U.S. Government connived in it still appears utterly implausible and has, of course, been denied by U.S. intelligence services and the White House.

Initially — like most people in America and Britain, including Matt Campbell — Professor Griffin dismissed any notion that the attacks were an inside job aimed at triggering the war on terror.

It was a year later that he changed his mind, when he was writing about American imperialism and 9/11 for his latest academic work.

This week a team of experts said that fire could not have caused the collapse of WTC7 (circled), adding further fuel to conspiracy theories

As part of his research he had come across a ‘timeline’ of the day’s events based on newspaper and television accounts. It raised several anomalies that caused him to doubt the official version of events. And, however outlandish it seems, his argument bears consideration.

One of the most puzzling anomalies was that none of the hijacked planes was intercepted by fighter jets, even though there would have been plenty of time to do so and 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. Then there were the irregular stock market dealings before the tragedy.

An extremely high volume of ‘put options’ — bets on the price of shares falling — were purchased for the stock of Morgan Stanley Dean Witter, the international financier that occupied 22 storeys of the World Trade Centre.

Even more remarkable was the volume of ‘put options’ traded on American and United Airlines, which operated the four aircraft hijacked by the terrorists.

On these two airlines, and only these, the level of share trade went up by 1,200 per cent in the three days before the catastrophe. As the shares dropped in response to 9/11 the value of these options multiplied a hundredfold. Someone, somewhere, made $10 million in profit.

But, of all the conundrums, the most perplexing is how the three World Trade Centre towers fell to the ground.

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

This explanation has been repeated in White House briefings, official inquiries into 9/11, leaks by the U.S. intelligence services and almost every TV documentary on the attack in the U.S. and the UK.

However, sceptics say the science does not stand up. They argue that steel does not begin to melt until it reaches around 2,800f, and open fires of jet fuel — such as those in the Twin Towers inferno — cannot burn hotter than 1,700f.

Official reports state the steel in the third tower reached a maximum of 1,100f.

Professor Griffin and other sceptics believe the Twin Towers were deliberately blown up. They claim their controversial theory is corroborated by first-hand testimony from firefighters at the scene.

In oral histories of 9/11 by New York Fire Department staff which have been made public, almost a quarter suggest they heard explosions going off before the World Trade Centre towers collapsed. Of the South Tower, firefighter Richard Banaciski said: ‘There was just an explosion. It seemed like on television when they blow up these buildings. It seemed like it was going all the way round like a belt . . . all those explosions.’

Colleague Kenneth Rogers heard them, too. He said: ‘There was an explosion in the South Tower. Floor after floor after floor. One floor under another after another . . . I figured it was a bomb because it looked like a synchronised kind of thing.

And Fire Captain Dennis Tardio recalled: ‘I hear an explosion and I look up. It is as if the building is being imploded from the top floor down, boom, boom, boom. I stand in amazement. I can’t believe what I am seeing. The building is coming down.’

But a more extraordinary challenge to scientific reason would happen on the day of the attacks in respect of the third tower, WTC7, which contained the offices of the secret service, and then mayor Rudy Giuliani’s emergency command centre, fitted with bullet- and bomb-resistant windows as well as secure air and water supplies.

In 2008, a U.S. Government-ordered report by the prestigious National Institute of Standards and Technology (NIST) concluded a six-year probe into the WTC7 attack.

Bystanders interviewed by U.S. television that day said there were ‘bang, bang, bang’ sounds before it fell down. Yet NIST insisted there was ‘no evidence’ of a controlled explosion.

The fall was provoked by fires on multiple levels. The heating of floor beams and girders had caused a critical support column to fall, initiating the fire-induced progressive collapse that brought the building down.

This week, eminent Alaska University engineers dismissed this explanation. Dr J. Leroy Hulsey, Chair of the university’s Civil and Environmental Engineering Department, said: ‘Fire did not and could not have caused the failure of this building.’

Griffin adds: ‘We are led to believe that for the first time in the known universe, a steel-framed, high-rise building was brought down by fire without the aid of explosives or incendiaries.

‘More clearly miraculous was the precise way in which WTC7 collapsed [straight down, with an almost perfectly horizontal roofline] into its own footprint. This is the kind of free-fall implosion that can only be caused by a world-class demolition company.’

But there is another perplexing matter regarding this third building. It concerns the bizarre TV reports in the U.S., and the rest of the world, that it had collapsed when it was clearly still upright — announcements made 23 minutes before it had actually fallen down.

One piece of BBC World footage shows a studio anchor talking to news correspondent Jane Standley, who is standing in front of the clearly visible WTC7 tower.

The anchor says: ‘The 47-storey building, situated very close to the World Trade Centre, has also just collapsed. It seems that this was not the result of a new attack. It was because the building had been weakened during the morning attacks.’

Then, oddly, the link to Standley breaks up and is lost.

Of course, this may just be a mistake made on one of the most hectic news days ever. Certainly, the BBC seems to think so.

In a statement made in 2007, a spokesman said: ‘In the chaos and confusion, I am sure we said things which turned out to be untrue or inaccurate, but at the time were based on the best information we had. We no longer have the original tapes of our 9/11 coverage, for reasons of cock-up, not conspiracy.’

This response — and the question of why the BBC announced the fall of WTC7 before it actually happened — has enraged those fighting for the ‘truth’, such as Matt Campbell. They say a series of 9/11 documentaries put out by the BBC have not been impartial or scientifically accurate.

It is why he, and other Britons who disagree with the official version of 9/11, have chosen to make their protest outside BBC headquarters on Monday.

This unlikely rebel, a trained theoretical physicist, former IT expert in the City, and now a reflexologist, has refused to pay his BBC licence fee for the past four years.

He claims: ‘The BBC has presented information to the public that breaks its own editorial guidelines. In at least one documentary, it removed the sounds of huge explosions going off in WTC7 moments before its collapse.

‘I think my brother Geoff and many others were murdered in an event that conflicts with what we have been officially told.

‘I believe there has been BBC complicity in a deliberate cover-up about how thousands died on that day nearly 16 years ago,’ he said yesterday as he braced himself for the sad anniversary.