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One of the London Bridge attackers was a follower of the banned al-Muhajiroun network. But has the UK been guilty of not taking the Islamist group seriously enough?

The man in a white robe with the microphone at the front of the hall addressed his audience of al-Muhajiroun supporters. Even with cameras there, he didn't hold back.

"When Tony Blair came out, George Bush came out at the same time and he said: 'Are you with us or you're with the terrorists?' What did we Muslims say?"

He paused for effect.

"We're not with you, we're with the… terrorists." The audience finished his sentence for him and cries of Allahu Akbar [God is great] echoed around the room.

It was April 2004 and I'd been invited to film at an al-Muhajiroun meeting at a community hall in Bethnal Green in east London. I was following a convert to Islam called Sulayman Keeler - born Simon Keeler - for a film I was making for Newsnight.

The next speaker was no less extreme. Abu Uzair, real name Sajid Sharif, took the microphone. The engineering graduate from Manchester launched into one of al-Muhajiroun's favourite topics - the 9/11 attacks on America.

Image caption Abu Uzair defends the 9/11 attack at an al-Muhajiroun meeting in 2004

"When the two planes magnificently run through those buildings… people say, 'hang on a second, that is barbaric. Why did you have to do that?' You know why? Because of ignorance."

At this point, I put my hand up to interrupt, asking him how it could be justifiable to call the killing of innocent people in the Twin Towers "magnificent".

Abu Uzair replied: "For us it's retaliation."

I pressed on: "But the killing of innocent civilians can't be right."

Jabbing his finger at me, Abu Uzair answered: "It can't be right according to you. According to Islam it's right. Do you not kill innocent civilians in Afghanistan?"

"I wouldn't call that magnificent," I ventured.

Abu Uzair replied: "Islamically speaking it's magnificent."

And with that exchange, the extreme, aggressive ideology of al-Muhajiroun became clear. It was a message of defiance, of hate. No compromise.

For them Islam was at war with the West. They knew our camera was rolling but they were justifying violence. This was a year before the London bombings on 7 July 2005 that claimed 52 lives.

The BBC understands that Abu Uzair has never faced legal action in the UK. He gave this lecture 13 years ago. The legal picture has changed now.

New laws ban the glorification of terrorism and there've been many more successful prosecutions over the past decade.

After the Manchester Arena bomb attack last month, MI5 let it be known that the scale of the threat from militant Islamists is huge.

Some 3,000 people in the UK are assessed to have current links to violent Islamist extremism, with another 20,000 assessed to have had recent links. That makes for a longlist of 23,000 people - the population of a small town.

Image copyright PA Image caption Radical preacher Omar Bakri Muhammad, pictured in 1996

The fact that al-Muhajiroun was allowed to recruit in towns across the UK for years, largely unfettered by the state, is part of the picture.

The group was the creation of the extremist preacher Omar Bakri Muhammad. Born in Syria, he was expelled in 1977 for his anti-Baath Party views and travelled to Lebanon where he joined Islamist group Hizb ut-Tahrir. Their aim was to create a single Islamic State - a caliphate - across the entire Middle East and, eventually, the world.

After a brief stay in Egypt, Bakri Muhammad settled in Mecca in Saudi Arabia. In 1983, he created a new group there called Jamaat al-Muhajiroun. The name means "the community of the emigrants".

In 1986, Bakri Muhammad's extreme Islamist views and connections to the banned Hizb ut-Tahrir led the Saudis to expel him. He fled to the UK where he was given asylum. He immediately created a UK branch of Hizb ut-Tahrir and began an aggressive recruitment drive among young British Muslims.

In the UK, Bakri Muhammad's sermons called for the black flag of Islam to be hoisted over Downing Street and for a global caliphate. The next decade was spent peddling his narrative - that Muslims were the victims of international conspiracies, that Sharia [Islamic law] must come to the UK.

But Hizb ut-Tahrir's international leadership grew tired of the man who would become known as the Tottenham Ayatollah, a reference to his office in north London. His focus on the UK was seen as a distraction from the wider goal of establishing a caliphate across the Middle East.

He was expelled from the party in 1996. And that prompted him to set up a new group in the UK - al-Muhajiroun.

In the late 1990s, Bakri Muhammad toured towns and cities with large Muslim populations in a recruitment drive for his new group. He was largely unchallenged by the British state, which had been preoccupied by the threat posed by Irish republican groups.

Image copyright Getty Images Image caption 2002: A demonstrator at an al-Muhajiroun event in London

They dismissed Bakri Muhammad as a fool. In the wider community, few realised how divisive and dangerous his views were.

Over the years, I've spent a lot of time in Crawley, investigating terrorism for the BBC. With its well-kept houses and leafy streets, this Sussex new town seems an unlikely recruiting ground for jihad. But some of the UK's most notorious Islamists were born there.

Three of those later convicted of planning to detonate a huge fertiliser bomb in 2004 grew up in the town. The leader of the plot, Omar Khyam, had strong links with al-Muhajiroun.

Image copyright PA Image caption Jawad Akbar and Omar Khyam (r) were given life sentences in 2007 for plotting bomb attacks

Omar Khyam and another of the fertiliser bomb plotters, Jawad Akbar, both attended Hazelwick secondary school in the town. At one point Bakri Muhammad managed to get himself invited to talk to sixth formers there.

The headteacher of Hazelwick school at that time was Gordon Parry.

"At the time our involvement with him was simply to promote religious tolerance and understanding and inclusivity," he says. "I will put my hand up now and say that was an utterly naïve thing to do. But at the time I didn't understand what he represented."

Fast-forward to 2017 and the terror attack at London Bridge had a strong link with al-Muhajiroun. The attack leader Khuram Butt was a supporter of the network, even appearing in a Channel 4 documentary last year called The Jihadis Next Door.

Image copyright Getty Images Image caption Police officers on the scene after the London Bridge terror attack on 3 June

Butt didn't exactly hide his extremist sympathies, and this raises a huge question for the British state - was the threat posed by radicals linked to al-Muhajiroun underestimated for years?

One senior former government adviser on the threat from terrorism certainly thinks it was. Richard Kemp was chairman of the Cobra Intelligence Group at the time of the London bombings in 2005. He was responsible for co-ordinating intelligence from the Security Service MI5 and the Secret Intelligence Service MI6, reporting to the secret Cobra committee that briefs the government on national security at times of crisis.

Image caption Col. Richard Kemp: "We've been far too tolerant of al-Muhajiroun"

"We've been far too tolerant of al-Muhajiroun," says Kemp. Their use of abusive language and threats was not tackled, he suggests.

"It was a major failure and we've seen the consequences - we've seen Lee Rigby [murdered] by a follower of al-Muhajiroun, we've seen numerous attacks around the world."

Kemp, also a former commander of British armed forces in Afghanistan, says there was a certain amount of complacency about al-Muhajiroun, both in the intelligence community and in successive governments. "There was a real failure politically and among the police and intelligence services to understand the way this situation was going to develop."

There was a period of inaction on the part of the authorities before 9/11 - but also after - that was extremely dangerous, Kemp believes.

Image copyright Getty Images Image caption The 9/11 attack on New York's World Trade Center

"The networks and the individuals involved in them saw that we were weak. They saw that we wanted to appease them and we wanted to let them continue and they exploited that - in terms of developing and building a network.

"There was an element of complacency among those people who were monitoring their activities. I certainly heard words used like 'blowhard' and 'windbag' in relation to some cases… that we're looking at people who talk a big war but don't actually fight it and don't pose a big threat to the UK."

Peter Clarke, the former head of counter-terrorism at the Metropolitan Police, doesn't agree with this analysis.

"It is easy to say with hindsight that more should have been done sooner to focus on the Islamist threat. This is too simplistic. The Good Friday agreement may have been signed in 1998, but the dissident republicans of the Real IRA were attacking targets on the mainland UK, including the BBC, until 2001. At that time Islamist groups were involved in low-level criminality to raise funds to send back to political organisations in their countries of origin."

Mr Clarke says he never heard the term "blowhard" being used.

Image caption Peter Clarke, former head of counter-terrorism at the Metropolitan Police

In 2004 it was clear the threat had escalated. An intercepted electronic communication about perfecting the ingredients for a massive fertiliser bomb prompted a huge counter-terrorism investigation by the police and MI5 - Operation Crevice. This was followed a few months later by another big investigation, Operation Rhyme, to foil a second Islamist bomb plot in the UK.

There was a race to investigate these plots, Clarke says. "These were both intercepted as a result of intensive investigation by MI5 and police, and preceded the 7/7 attacks. So it is not right to say that the Islamist threat was ignored.

"Priorities were chosen according to the threat posed by various groups. After 9/11, Irish terrorist groups pulled back on their activities, allowing a shift in focus towards finding out if Islamists did indeed pose a threat."

The fertiliser bomb plotters - and the 7/7 London bombers who murdered 52 people the following year - also had strong links to al-Muhajiroun.

Image copyright Guzelian Image caption Mohammad Sidique Khan, one of the bombers in the 7/7 London attacks in 2005

By 2004, it was clear that the al-Muhajiroun network had been at the very least a gateway to terror.

Al-Muhajiroun and its leaders always played a cat and mouse game with the state. Bakri Muhammad wound up the group in 2004 because he thought it was about to be banned.

But the network then launched a series of groups which were, in effect, different names for the same thing.

Al-Ghurabaa and the Saviour Sect both emerged in 2005 as splinter groups, and were proscribed in 2006. Other groups created by the same network included Muslims Against Crusades, Islam4UK, Shariah4UK, Call to Submission, Islamic Path, the London School of Sharia, and Need4Khilafah. All of them were proscribed by the government after they emerged.

All of these groups can be considered as the al-Muhajiroun network. They all wanted to see Sharia law introduced to the UK by force, do not believe in democracy, and have hostile views about Shia Muslims and other minorities that they claim are consistent with the teachings of the Koran.

So why was more not done? This was ideological extremism and the leaders of the network, like Anjem Choudary, were always careful to stay, just, on the right side of the law so they could not be arrested.

Image copyright Getty Images Image caption Anjem Choudary, one of the co-founders of al-Muhajiroun, currently jailed for supporting IS

"No-one knew whether the ideological stance of al-Muhajiroun was going to inevitably lead to violence in this country," says Mr Clarke. "Once the threat from dissident republicans receded, the focus on the Islamist threat grew very quickly. It's also probably fair to say that no-one had before encountered a terrorist threat that was rooted in ideology rather than political goals, that knew no boundaries and for whose adherents capture or death was not a risk but an aspiration."

The British state did take action. Bakri Muhammad was stopped from re-entering the UK after the 7/7 bombings in London in 2005, moving back to Lebanon, where he is serving a prison sentence for terrorism offences today. But his network continued under different names.

Image copyright Getty Images Image caption Flowers left near the spot where serviceman Lee Rigby was murdered in 2013

The network's supporters have been linked to terror plots across the world. And a number of adherents in the UK have been imprisoned. In addition to the five fertiliser bomb plotters - Omar Khyam, Jawad Akbar, Waheed Mahmood, Anthony Garcia and Salahuddin Amin - other followers such as Sulayman Keeler and Abu Izzadeen have been convicted of terror-related offences. Figurehead Anjem Choudary was eventually jailed for five years for inviting support for so-called Islamic State.

2003: Suicide bombing attack on Mike's Place bar in Israel

2004: Fertiliser bomb plot and Operation Rhyme in the UK

2005: London bombings

2013: Murder of Lee Rigby

2014: Suicide bombing attack in Iraq by Waheed Majid

2017: London Bridge attacks

This latest connection, between the recent London Bridge terrorist attack and al-Muhajiroun, is likely to feature in the ongoing police investigation.

We know Khuram Butt, the attack leader, was a long-term supporter of the group. But if you dig a little further some interesting facts emerge about the gym in east London where he used to train - the Ummah Fitness Centre in Ilford.

Image copyright Metropolitan police Image caption Khuram Butt, one of the London Bridge attackers, had connections to Al-Muhajiroun

Newsnight discovered that a man called Sajeel Shahid applied for planning permission to create a gym for Muslims from warehouse space in 2011.

To understand the significance of this, we have to look back to the late 1990s when Omar Bakri Muhammad set up a branch of al-Muhajiroun in Pakistan. Sajeel Shahid is alleged to have helped run the office in Lahore.

Just after the 9/11 attack, an American jihadist called Mohammed Junaid Babar joined them. Three years later, he turned against his old friends and became a jihadi "supergrass", testifying against people in the al-Muhajiroun network who went on to plan a terror attack in the UK.

We obtained a confidential transcript of the FBI's interview with Junaid Babar. In it, Junaid Babar tells the FBI that Sajeel Shahid was the leader of al-Muhajiroun in Pakistan. The document alleges that Junaid Babar said that Sajeel Shahid co-ordinated training for jihadi recruits at a camp in Pakistan where they "most likely received explosives training".

Junaid Babar also said in court, during the 2007 trial of the fertiliser bomb plotters, that in February 2003 he and Sajeel Shahid had found a good location for weapons training in Pakistan's north-west frontier province near the town of Malakand. The future leader of the fertiliser bomb plot, Omar Khyam, and the future leader of the London 7/7 bombers, Mohammad Siddique Khan, trained there.

We tried to contact Sajeel Shahid to ask him about this, but a man answering the phone number we had simply said it was the wrong number and hung up. There's absolutely no suggestion that Sajeel Shahid had a hand in the London Bridge attack, and he has never been charged with any terror-related offence. Sajeel Shahid has previously denied being the leader of al-Muhajiroun in Pakistan and said that he had only been a student in the country.

Image caption Sajeel Shahid being interviewed by the BBC in London in 2007

The named groups connected with al-Muhajiroun have been proscribed, but the networks of supporters persist.

After the recent spate of attacks, Prime Minister Theresa May said "enough is enough" and declared her intent to do something about it.

But based on the last two decades of various governments failing to get on top of the problem of radicalisation, Richard Kemp remains worried. "I'm not sure that there is a political courage or the political will."

Richard Watson's report for Newsnight can be seen on BBC iPlayer