Former Guantanamo Bay detainee Moazzam Begg walked free from jail on Wednesday after a string of terrorist charges linked to the civil war in Syria were dramatically dropped

Soon after the Gulf War ended Saddam Hussein's tyranny, a secret memo about a dangerous British prisoner held in Guantanamo Bay detention camp was sent to America's military top brass.

It landed on the desks of officers at the U.S. Defence Department in Miami in November 2003 and was signed by Geoffrey D. Miller, the commander of the camp in Cuba, which was notorious for incarcerating suspected Islamic terrorists from all over the world without trial.

The memo said that prisoner UK-000558 (a number tag detailing his country of origin) had been picked up by American secret services during a raid at his rented family home in Pakistan, before being transferred to Guantanamo Bay for interrogation.

He was, asserted Major General Miller, a member of Al Qaeda, a 'high threat' to America and her Allies, and should not be set free. The prisoner's detailed knowledge about terrorist training camps he had attended in Afghanistan and Pakistan during the 1990s meant he was also of 'significant intelligence value' to the West.

We only know about this highly confidential memo because it emerged among 779 military intelligence files relating to Guantanamo prisoners discovered and posted online by Wikileaks three years ago.

Prisoner UK-000558 was actually Birmingham-born Moazzam Begg, who was held in Guantanamo after being arrested in Pakistan in February 2002.

He was released in 2005 without charge, along with three other remaining Britons in the detention camp, following 'intensive and complex' negotiations between the British and U.S. governments.

On his return to this country, he became a passionate campaigner on behalf of Guantanamo prisoners, a vocal critic of Western foreign policy in the Middle East, and a hero to thousands of followers.

Scroll down for video

Fast forward almost a decade to this week and Begg was, once again, emerging smiling from jail.

This time, it was from London's Belmarsh Prison after a terrorism case against him — due to begin at the Old Bailey next Monday — was abandoned by police and the Crown Prosecution Service.

Begg was held in Guantanamo after being arrested in Pakistan in February 2002, but was released without charge in 2005, along with three other remaining Britons in the detention camp

He denied seven charges of terrorism, including attending a training camp in Syria between 2012 and 2013

This time he had been charged — on seven counts related to terrorism, all of which he denied, including attending a terrorist training camp in Syria between 2012 and 2013, possessing terrorist-related documents and helping to fund terrorism.

Then, astonishingly, the case was suddenly dropped at a pre-trial hearing on Wednesday.

In one of the most embarrassing fiascos for the security services in recent years, at the last minute 'new information' fatally undermined the prospect of a successful outcome of the trial for the police and the CPS.

It appears that MI5 belatedly produced documents that revealed their extensive contacts with Begg before and after trips he made to Syria in recent years.

They included minutes of meetings that MI5 officers and lawyers held with him at which he discussed his travel plans and said he was assisting opposition fighters in their war against President Assad's regime.

The farcical collapse of the case as he watched via a video link from Belmarsh, where he has been incarcerated for the past seven months, took even the heavily-bearded Begg by surprise.

'To be honest, I wanted my day in court,' he said on Wednesday, before being driven back home to his wife and four children in Birmingham. 'But I was very happy when I heard the news.'

'New information' fatally undermined the prospect of a successful outcome of the trial for the police

Needless to say, 46-year-old Begg's freedom has delighted his supporters in the Muslim community, who have protested his innocence ever since he was arrested in February this year.

The one-time Islamic bookshop owner and human rights activist has become one of the UK's most high-profile Muslims since the 'war on terror' was launched after the attack on the Twin Towers in 2001. And this latest episode — in which once again he has made a fool of the authorities — can only increase his stature.

Speaking from outside prison on his release, he said: 'Not once, but twice in my case, this Government has been involved either in directly detaining me or indirectly detaining me, and on both occasions it's been unlawful.'

So who is Moazzam Begg? And how did he come to be such a thorn in the side of the intelligence agencies in their fight against terrorism?

Begg was born in the Midlands to respectable middle-class parents. His father, a bank manager, emigrated here from Pakistan and the family were the first Asians to settle in their Birmingham street. Begg was sent to a Jewish school in the city because 'it was the next best thing' to a Muslim education.

His release has delighted his supporters in the Muslim community, who have protested his innocence ever since he was arrested in February this year

An inmate at Guantanamo Bay being led handcuffed by guards at the detention facility

Yet in his teens he was already brushing with the law, joining the multi-ethnic Lynx street gang to fight skinheads intent on violence against immigrants, and particularly those from Pakistan.

Eventually, in his 20s, he gave up the gang and began working for a family grocery company.

But he also became increasingly interested in Islam, especially after holidays to visit family in Pakistan, where he was invited to visit a training camp for Muslim fighters who were sympathetic to Al Qaeda and the Taliban.

From there on, many of the stories about the well-spoken and articulate Moazzam Begg descend into hearsay. He has always strenuously denied ever being involved in terrorism, although this is starkly at odds with the signed statement he gave to FBI agents after his capture in Pakistan.

In this, Begg admits to having attended three separate Al Qaeda terrorist training camps in Afghanistan, where he learned to fire AK-47 rifles and rocket-propelled grenades, and use primitive explosive devices.

He also said that, when living in Britain and running his Islamic bookshop in Birmingham, he acted as a 'communications link' between radical Muslims in the UK and others living abroad.

The bookshop, he told the FBI in a statement, was a focal point 'for assisting Islamic militants by spreading Islam and recruiting individuals for global jihad'.

The shop was raided by MI5 in 2001 and Begg was questioned about the possession of an illegal weapon and illegal terrorism activities.

It was after this incident that he and his family moved to Afghanistan and, then, Pakistan, where he was arrested by the FBI.

He was taken first to the U.S. military detention centre at Bagram — where he says he was abused, which the Pentagon denies — and then to Guantanamo.

Today, he lives comfortably with his wife and four children in a £400,000 house in one of the smarter suburbs of Birmingham.

The source of his money? A controversial Government compensation payout in 2010 to former Guantanamo detainees, which saw Begg receive £1 million after successfully claiming that Britain was complicit in his original abduction by U.S. intelligence services, and then his mistreatment at Bagram camp in Afghanistan.

The fact is that MI5 has flirted with Begg for years (even allegedly trying to recruit him as an undercover spy), despite — or perhaps because of — their suspicions he has a shadowy past with alleged links to Islamic terrorism.

They have not only held meetings with him in secret, and monitored his blogs and emails, they have sent their operatives to listen as he makes his speeches up and down the country.

Indeed, a blog published by Begg before he was charged in February explains exactly what MI5 knew all the time. He wrote: 'In October 2012, I was called by an MI5 officer who said he wanted to talk to me about my views on the situation in Syria after reading an article I had written.

'I told him I was investigating several leads regarding British and American complicity in rendition and torture in Syria. MI5 called back after consulting with their lawyers, and said they understood that and would still like to meet.

'I agreed to speak to them at a hotel in East London. Both MI5 and I had our lawyers present.' The blog continues: 'MI5 was concerned about the possibility of Britons in Syria being radicalised, and returning to pose a potential threat to national security.

'I told them that Britain had nothing to worry about, especially since British foreign policy, at the time, seemed in favour of the rebels (against President Assad).

'At the end of the meeting I was assured by MI5 that my proposed return to Syria to continue my work would not be hindered.

'Subsequently, I travelled to Syria without incident.

'I witnessed the squalid refugee camps, I visited the wounded — young and old, some of whom I buried; I saw the carnage of the killing machine and I saw the beautiful young faces of children aged beyond their years.

'I witnessed the harsh winter and saw farmers chop down their olive trees to warm themselves and I heard the horror stories of torture …

'I also saw aid coming in from all over the Muslim world, which included British ambulances, fire engines, garbage disposal trucks.

'There were British aid centres and hospitals with British doctors, and volunteers from Britain's Muslim community. And yes, there were some British fighters, too . . .'

Yet despite MI5's apparent assurance to him that he would be left unhindered, Begg's passport was seized when he was stopped at Heathrow Airport last December as he returned from a trip to South Africa for a service to commemorate the life of Nelson Mandela.

'I was told my previous visits to Syria had constituted involvement in terrorism,' he wrote in a subsequent blog, before being sent to Belmarsh jail.

And there the matter rested until this week.

So what exactly was the reason for the 11th-hour abandonment of what was going to be a high-profile trial? Was it that MI5's contacts with Begg and broken assurances to him undermined the case for the prosecution?

Or could Begg's release be linked to something else? To a behind-the-scenes deal to free British hostages held by the Islamic State in Syria, for instance?

One of the hostages is, of course, Alan Henning, the non-Muslim Manchester taxi driver who was seized while travelling to the strife-riddled country on a convoy run by a charity group, Rochdale Aid4Syria, which had actively campaigned for Begg's release from Belmarsh on its Facebook page and other websites.

There are lurid — and unconfirmed — rumours that some members of the charity were sympathetic to hard-line Islam, and even Islamic State itself.

The charity, and others in Lancashire, have already come under MI5 scrutiny for naming a fire engine on an earlier aid convoy to Syria after a female terrorist, Aafia Siddiqui, who is dubbed 'Lady Al Qaeda' by counter-terrorism police.

Siddiqui is serving an 86-year sentence in America for trying to shoot two U.S. soldiers after being arrested in Afghanistan in possession of bomb-making instructions.

Islamic State demanded Siddiqui's release in exchange for the life of U.S. hostage and journalist James Foley, who was beheaded six weeks ago.

Do our intelligence services think Begg's freedom will be a lever to get Alan Henning's release?

Do they believe he possesses secrets that will help them in the fight against Islamic terror in this country and abroad?

Do they think — just as the U.S. Major General at Guantanamo Bay did of prisoner UK-000558 — that Begg is of 'significant intelligence value' to the West.

We cannot know, of course. And this week, after the trial's collapse, MI5 was staying predictably silent.