US security officials claim the level of al-Qaeda activity in the UK poses a major security threat at home and abroad. State Department officials believe the UK is vulnerable to being used as a base for al-Qaeda terror attacks.

They claim the growing presence of the terrorist network in Britain is now a major security concern for other Western countries.

The comments come as the US investigates the failed attempt to blow up a transatlantic jet over Detroit on Christmas Day, by Umar Farouk Abdulmutallab, a Nigerian who studied at University College London.

Abdul Mutallab has been linked to al-Qaeda groups in Yemen, but there are claims he became radicalised while studying at UCL and living in London between 2005 and 2008.

The US security community has previously expressed concerns over the growing number of Islamic radicals in the UK, dubbing the capital ‘Londonistan’.

The UK is now believed to have the highest concentration of al-Qaeda sympathisers of any Western country.

A US state department official told a newspaper today that the high levels of al-Qaeda activity in Britain is becoming a major source of concern for them.

He added: “The organisation’s ability to use Britain as a base to plot terror attacks constitutes a serious threat to the security of Britain and other Western countries.”

Abdul Mutallab tried to detonate a mixture of explosives strapped to his upper thigh while on flight 253 from Amsterdam to Detroit on December 25.

The home made bomb failed to explode but set fire to the 23-year-old’s leg, alerting his fellow passengers who managed to apprehend him as the plane landed.

The attempt drew comparisons with “shoe-bomber” Richard Reid who planned to blow up a commercial flight with explosives hidden in his shoe.

Reid, a British citizen from South London, claimed he was a member of al-Qaeda and is currently serving a life sentence in a US prison.