“We must wage war against the disbelievers who dominate our lives. If you cannot make a bomb, there are then other weapons; certainly a simple knife from your local B&Q will do the job”, declared the fighter from Al-Shabaab in a video celebrating the murder of soldier Lee Rigby.

Raising a Kalashnikov assault rifle, the masked man went on to talk about the UK cities and towns from which the Somali terrorist group had drawn jihadists. Birmingham came top of the list.

This was in 2013 and by then Birmingham already had the distinction of being the birthplace of the UK’s first suicide bomber; the city where the country’s first al-Qaeda plot was hatched and also of being the home of one of the financiers of the 9/11 atrocity.

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Last night police carried out a series of raids in the city following the Westminster attack. Four arrests, out of eight nationwide, were made there. The car which was crashed into the railings outside the Houses of Parliament after mowing down people on Westminster Bridge was rented from a Birmingham branch of the firm Enterprise.

Isis said it was behind the murders of three people and injuries to a dozen others in the London assault, describing the attacker as a “soldier of the Islamic State”. However, the terrorist group routinely claims “credit” for such acts and the veracity of this cannot be established at this stage.

The spread of extremism in Birmingham had continued unabated since the Al-Shabaab video was posted. A study earlier this year estimated that one in 10 of all those linked to Islamist terrorism in Britain and abroad came from just five council wards in the city. Thirty-nine convicted terrorists came from Birmingham, which has a Muslim population of 234,000. The wards of Springfield, Sparkbrook, Hodge Hill, Washwood Heath and Bordesley Green supplied 26 of them.

It is a fact that surprises and raises concern that the numbers from Birmingham of those who had embraced extremist violence is more than those from West Yorkshire, Greater Manchester and Lancashire, which, between them, have a Muslim population of just under 665,000.

The Islamist alumni from Birmingham include Rashid Rauf, of British and Pakistani background, who was one of the ringleaders of a plot to blow up transatlantic airliners in 2006. He was arrested in Pakistan in December that year but the more serious charges of terrorism against him were reduced to forgery and possession of explosives in court. American officials complained that Rauf was being protected by elements in the Pakistani secret police, ISI, and the country’s military.

Rauf escaped, or was allowed to escape, from prison but was reportedly killed in a CIA drone strike in November 2008. There were, however, reports that he had claimed he was living in a fundamentalist enclave in North Waziristan.

Birmingham also produced Moinal Abedin, the UK’s first al-Qaeda inspired terrorist. He had attended a training camp in Pakistan, and, on his return, had turned his house in Sparkbrook into a bomb-making factory. When raided, it led to the discovery of an “industrial quantity” of the high explosive HMTD of the type used in the 7/7 London bombings. Abedin was jailed for 20 years in 2002.

Irfan Khalid, whose family came from Pakistan, was involved in a plot with the expressed aim of killing more than those who died in the 7/7 bombings. The ambition, according to secret recordings, was to inflict about 2,000 casualties. He was sentenced to 18 years in jail in 2013.

Others in the Islamist roll include Parviz Khan, jailed for life in 2008 for planning to kidnap and behead a British soldier on behalf of al-Qaeda and Abdelatif Gaini, Humza Ali, Mohammed Ali Ahmed and Gabriel Rasmus, who trained for jihad with paintballing sessions in Solihull. Humza Ali was later convicted of terrorism offences; Rasmus was jailed after being arrested en-route to Syria; Ali Ahmed was convicted for handing money over to a man linked to the Brussels bombing and Gaini is thought to be fighting for Isis in Syria or Iraq.

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Most of these men have family links to Kashmir, a state disputed between Pakistan and India. Many young men went to Pakistan to train to fight against Indian forces in Kashmir and some of them, say British and American security officials, were also channelled by their handlers in sections of the Pakistani security establishment, to other jihadist groups fighting elsewhere in the region, including Afghanistan. Some joined al-Qaeda and Isis.

Indoctrination took place in mosques which had been taken over by radical clerics and, it is claimed, a number of schools. Birmingham is in the centre of the so-called “Trojan Horse” plot in which, it is alleged, an organised group of Islamists sought to infiltrate and take over state education establishments.