Al-Shabaab: the growing menace of the al-Qaeda affiliate

Al Shabaab draws them in with the help of a sophisticated media arm which is thought to now have three to four people working on it full-time – among them a British Pakistani whose London accent is heard voicing documentary reports of military battles.

The group has also taken to Twitter where it engages in regular spats with spokesman for the Kenyan government, which late last year invaded Somalia.

"We believe there are a substantial number of Brits involved in al-Shabaab," Abdullahi Boru Halakhe, Hornof Africa Analyst for the International Crisis Group, told The Daily Telegraph. "The movement is using social media to market itself and using the narrative of the oppressed to attract recruits."

Al Shabaab itself is at present thought to be too absorbed with battles at home to focus on exporting its terror tactics.

But British security forces are paying close attention amid concerns that, given its newly-forged links to al Qaeda, a proponent of global campaigns, British recruits might bring their new-found terror skills to wreak havoc.

The most obvious target for such an attack is the London 2012 Olympics.

In 2010 Jonathan Evans, the head of MI5, said it was "only a matter of time before we see terrorism on our streets inspired by those who are today fighting alongside al Shabaab".