The Daily Telegraph A 21-year-old student from Ealing, West London has blown himself up as a suicide bomber in the war-torn country in the first reported incident of its kind.
Jonathan Evans, the head of MI5, voiced his concerns over increasing numbers of young men travelling to the East African country in an interview with the Daily Telegraph last month.
He talked of "networks that help individuals go and take part or provide support to extremist gangs in Somalia" and may return to attack Britain.
Michael Hayden, the outgoing head of the CIA, has said that the Ethiopian invasion of Somalia has "catalysed" expatriates around the world.
An audio message from Osama bin Laden last month urged Muslims to send money or go to Somalia to fight.
The student abandoned a course in business studies at Oxford Brookes University to join up with al-Shabaab [the Youth], an Islamic militia fighting the Somali government, according to Channel 4 news.
He crossed the border from Kenya and blew himself up at a checkpoint in the southern town of Baidoa in October 2007.
Ali Mohamed Ghedi, the Somali Prime Minister was staying at a hotel nearby and escaped unharmed but jihadi websites claimed that 20 Ethiopian soldiers were killed.
The man left a suicide video in which he said: "Oh my people, know that I am doing this martyrdom operation for the sake Allah.
"I advise you to migrate to Somalia and wage war against your enemies. Death in honour is better than life in humiliation."
Sheikh Ahmed Aabi, a moderate Somali leader in north London, said he knew of the case and had heard of other young men travelling to Somalia to join radical groups.
"I'm hearing it from parents," he said. "They say [their children] are joining the jihad. I am hearing there are a lot of people.
"This is a big problem facing our community."
Peter Neumann, a terrorism expert at King's College London, said: "The numbers I hear [going from Britain to Somalia] are 50, 60, or 70 but in reality we don't know.
"You don't need big numbers for terrorism. Somalia will never become another Pakistan but that does not mean it is not a threat."
One young man outside a west London mosque was adamant it was his right to go to Somalia to fight.
He said: "If American troops can go from Arizona to Iraq then someone can leave this area and go to Somalia."
While travel to and from Pakistan remains the major concern for the security services, Britain is also home to the largest Somali community in Europe, estimated at over 100,000.
Two of the failed July 21 bombers, Yassin Omar and Ramzi Mohammed, arrived in Britain from Somalia as refugees although they were radicalised after their arrival.
Ethiopian troops invaded in December 2006 to oust a government formed by the Islamic Courts Union and withdrew only last month.
Al-Shabaab, designated as a terrorist group in the US, aims to introduce sharia law to Somalia and took control of Baidoa last month.
