He says the radical Islam they preach inspires terrorists to violence

Expert says group were not taken seriously enough for too long

Government has banned them but they morphed into other organisations

Group linked to more than 20 plots or attacks carried out since 1997

Half of the terror attacks carried out or plotted in Britain involve members of just one extremist network, a new report reveals.

Al-Muhajiroun, a banned organisation once fronted by hate preacher Anjem Choudary, has been linked to a series of atrocities and plots dating back to 1997.

A new book by terrorism expert Raffaello Pantucci has now found that since its formation in the 1980s, the group has been central to Islamic extremism in the UK.

More than 20 terror attacks plotted or carried out in the UK - including the 7/7 bombings which killed 52 people - have been linked to extremist network al-Muhajiroun in a new report

It is thought the first known violence directly linked to the group took place in 1997, when a member of the organisation attacked a police officer.

At least one of the bombers who carried out London's 7/7 bombings had met a key supporter of al-Muhajiroun, Omar Khyam, before the attacks which killed 52 people on underground trains and a bus in 2005.

Michael Adebolajo and Michael Adebowale, who murdered Fusilier Lee Rigby in a street in Woolwich, south-east London in 2013, had both attended events organised by the group.

Despite having been banned in 2005, the group has morphed to take on a series of other names, and its influence continues to be felt, with Brustholm Ziamani, who was sentenced last week for plotting an attack inspired by that on Lee Rigby, also having been inspired by al-Muhajiroun.

Research shows that out of 51 attacks and plots carried out or foiled in Britain, al-Muhajiroun had influence in at least 23.

Mr Pantucci, who studies extremism for defence forum The Royal United Services Institute, said the group sold its followers a radical interpretation of Islam which often inspired them to commit violence.

He told MailOnline: 'It is an oversimplification just to write them off as outcasts or losers, some of them have been involved in quite serious gang activity or crime in the past and end up finding this as a kind of redemption for their activity.

'You also have to remember that some of the top figures are quite charismatic people who are good at drawing people in and given them these very aggressive ideas.'

Hate preacher Anjem Choudary (left) was once a leader of the group before it was banned. Supporter Omar Khyam (right) met up with at least one of the London bombers before they carried out the 2005 attack

Al-Muhajiroun was set up by Omar Bakri Mohammed (left), pictured with radical cleric Abu Hamzu (right)

Mr Pantucci said that the group's influence had been underestimated in the past and hoped his book - whose title We Love Death As You Love Life is taken from quotation by one of the 7/7 bombers - would encourage politicians to crack down on the organisation and its spin-offs.

He added: 'These people are very good at being in the periphery and the background without ever having their hands on the device or being directly implicated in plots, which would see them given heavier sentences.

'I think constant disruption of the group is not a bad thing. By proscribing these groups you force them to change their name, their website, which inhibits them, also by arresting them on more minor charges you take them off the streets for a time.'

Al-Muhajiroun was set up by Omar Bakri Mohammed, a Syria-born Islamic extremist who lived in Britain from 1986 until he was banned from returning in 2005 after going to Lebanon.

Anjem Choudary, who remains in Britain, later became the public face of the organisation, which re-emerged as groups called Islam4UK and Need4Khalafah after it was banned.

Lee Rigby's killer, Michael Adebolajo (left) and Michael Adebowale (right), had attended the group's rallies