More than 4,000 British Muslims have passed through terrorist training camps in Afghanistan and Pakistan, according to security agencies, providing a fertile recruitment pool for the Islamist international jihad.

Men from the UK's Kashmiri community have joined groups such as Lashkar-e-Toiba, the prime suspects in the Mumbai attacks, which have been fighting against Indian forces in Kashmir. Others from a Pakistani background are in the ranks of the Taliban and other groups taking part in action against British and Nato forces in Afghanistan.

A former commander of the British force in Helmand, Brigadier Ed Butler, has revealed that his troops had come across British Muslims in southern Afghanistan. "There are British passport holders who live in the UK who are being found in places such as Kandahar," he said. "There is a link between Kandahar and urban conurbations in the UK. This is something the military understands, but theBritish public does not."

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Last year, RAF Nimrod intelligence-gathering aircraft tracking Taliban radio signals in Afghanistan heard insurgent fighters speaking with Yorkshire and Midlands accents.

As well as fighters joining their ranks, groups such as Lashkar also benefit from funds raised on their behalf in the UK by the Muslim community. It has also been claimed that some of the aid money donated for the earthquake disaster relief three years ago was siphoned off for militant groups.

Lashkar, previously known as Jaish-e-Mohammed, has forged links with al-Qa'ida in Pakistan and are said to have shared training camps. One of their most famous recruits was Rashid Rauf, accused of being a key member in the plot to blow up transatlantic airliners, who was recently reported to have been killed in an American missile strike.

British Muslim recruits have also been involved in other conflicts. Asif Hanif, 21, from London, killed three people and injured 55 by blowing himself up in Tel Aviv. A companion, Omar Sharif, 27, from Derby fled the scene after explosives strapped to his body failed to detonate and was later found dead, his body washed up on an Israeli beach.

Somalia's transitional government has accused Britain of being the main source of money and men for the fighters of the Islamist Courts Union (ICU), a fundamentalist group, in the country. The then deputy prime minister, Hussain Mohammed Aideed, declared: "The ICU's main support was coming from London, paying cash to the ICU against the government. Among those who died in the war with the ICU wereBritish passport holders."

The Independent, in Mogadishu after the Somali capital was taken over by Islamist forces last summer, discovered a significant number of young Somalis who had returned to fight for the Islamists from the diaspora in the West. Half a dozen young men, including two brothers from Wood Green in north London, were acting as bodyguards for Sheik Yusuf, one of the main Islamist commanders. One of the brothers, Hamid, said at the time: "The true Muslims are the only ones who are honest and who are patriots. We are doing our duty by fighting for the cause of Islam, which is above all countries."

Britain has also been accused of being the centre where a number of terrorist plots abroad were planned. Moutaz Almallah Dabas, a Syrian-born Spanish citizen accused of helping those who took part in the 2004 Madrid train bombings, was extradited from London to Spain after the discovery of links between the attack and an alleged cell in England.