No one has ever been prosecuted for membership of the UK’s 'most dangerous Islamist group' despite followers launching numerous terror attacks, it can be revealed.

The government banned ALM as a terrorist group in 2006, making membership a criminal offence punishable by up to 10 years in prison.

But a senior counterterror officer admitted that despite police identifying 600 current or former associates, none of them have been prosecuted for membership.

The Metropolitan Police officer, who is codenamed Witness M because of an anonymity order, told inquests into the London Bridge attack that suspects had been arrested but not charged.

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The coroner at the London Bridge inquest today cleared M15 and the police for missing opportunities to prevent the attacks, even though ringleader Khuram Butt had been monitored by security services as a known member of ALM.

The admission that no one has been prosecuted for membership of the group comes after more than a dozen people were prosecuted for membership of the neo-Nazi terrorist group National Action, despite setting up new factions under different names to evade the ban.

A survivor of the 2005 London bombings, which were carried out by terrorists linked to ALM, said she was concerned by the lack of prosecutions.

“It allows ALM to galvanise support and disseminate their messages,” Sajda Mughal OBE told The Independent.

“An inability to disrupt these activities leaves young people at the risk of radicalisation and society at grave risk of future attacks.

“As we fast approach the 14th anniversary of 7/7, I am disappointed that little progress is being made to bring about the end of a terrorist organisation that has caused such pain and anguish to the lives of many.”

Witness M insisted that police would act on evidence of someone being a member of ALM but the “nature of that group doesn’t necessarily present us with those evidential opportunities”.

He said there were no membership lists, official branding or iconography that could be used to prove a link, and ALM did not claim responsibility for attacks by its followers.

“They’re well known as being an organisation that is a pathway to radicalisation and there are a number of individuals who have gone on to commit attacks,” he told the Old Bailey.

“They’ve never been underestimated and there’s never been anything other than a concerted effort around that organisation.”

Even leader Anjem Choudary, a former lawyer, has not been prosecuted for membership and was instead jailed for inviting support for Isis (EPA)

ALM has changed its name numerous times to evade the 2006 ban, and a police operation seen as a test case ended in failure.

Scotland Yard detained 24 activists protesting outside London’s US Embassy in December 2011 for membership of a proscribed group, but they were all released without charge following consultation with the Crown Prosecution Service (CPS).

Theresa May had banned ALM’s latest incarnation – Muslims Against Crusades – the month before but the same extremists were able to continue their activism by calling themselves United Ummah.

A recent report hailed ALM as Britain’s “most prolific and dangerous extremist group” because of its role in radicalising terrorists who have committed or plotted numerous atrocities.

London Bridge ringleader Khuram Butt was a member, Westminster attacker Khalid Masood had links to cells, and ALM supporters committed a quarter of all Islamist-related offences in the UK between 1998 and 2015.

There are fears that the group is regenerating following the release of several activists from prison.

Choudary is among those freed in recent months, after being jailed for stand-alone terror offences including inviting support for Isis and disseminating terrorist propaganda.

Several released extremists are under restrictions or probation supervision, but authorities could be powerless to stop ALM restarting its old tactics of incendiary protests and street preaching.

David Videcette, who worked in Scotland Yard’s counterterror branch from 2004 to 2010, said ALM used freedom of speech to defend its activities against crackdowns.

“Choudary is a trained lawyer, he’s not stupid, and we were always one step behind him,” he said.

“I think sadly we will see a resurgence with ALM. We will see people travelling and carrying out attacks.”

Al-Muhajiroun supporters at a 2013 protest organised by Anjem Choudary under the name the ‘Shariah Project’ in Brick Lane, London (Reuters) (REUTERS)

Mr Videcette said social media and modern communications could make it easier for officers to prove membership.

But he warned that even if police have enough evidence to detain a suspect, they can be prevented by MI5 because of intelligence operations.

Michael Kenney, who was in contact with ALM activists for his book The Islamic State in Britain, said they went to lengths to hamper potential prosecutions.

“They have now moved away from platform names entirely so I’m not sure what the police would do,” he told The Independent.

“They’re being very careful at this point – they want to see what they can get away with.”

Mr Kenney, a University of Pittsburgh professor, said ALM had not changed its ideology or efforts to “prepare British society for the coming of the caliphate and living under Sharia”.

He said that although the 2006 ban put pressure on the group, leaving it weakened and fragmented, some jailed members have emerged from prison with even more extreme beliefs.

“If they were jailed for membership the same thing would happen – I don’t think it would stop them,” Mr Kenney added.

The independent reviewer of terrorism legislation, Jonathan Hall QC, said banning groups allows authorities to subject members to orders that limit their communications and activities.

“The footprint of proscription goes beyond arresting people for membership,” he said. “It provides a gateway for the home secretary to make a terrorism prevention and investigation measure.”

Lord Carlile, a former independent reviewer of terrorism legislation, said the 600 ALM associates identified would include people who were “not involved in anything close to terrorism themselves”.

“Mass proscription arrests would not be evidentially feasible,” he added. “The services have to make judgement calls, and they are bound to get some of those judgement calls wrong some of the time.”

A spokesperson for the Metropolitan Police said: “It is categorically untrue that the Met does not seek to prosecute people who are members of ALM or indeed any other proscribed organisation.

“Where there is evidence a person is a member of a proscribed organisation, the Met will always investigate and seek a prosecution. The decision to charge an individual is made in liaison with the CPS.”

Jenny Hopkins, head of the CPS’s special crime and counterterrorism division, said: “The CPS can only consider a prosecution after a file of evidence is referred to us by the police.