In his end-of-year analysis of the dangers facing Britain, the chief of the defense staff, General David Richards, said the Arab Spring could stir unrest in Britain's immigrant communities.

"(There is) the risk that the Arab awakening leads to fissures and internal conflict that could be exported, including militant Islamism," Richards told a defense thinktank, the Royal United Services Institute, in London.

"They have diasporas reaching back to this country, as does Pakistan and other states struggling with instability."

A year after protests that led to the Arab Spring began, moderate Islamist parties have taken control in Tunisia and Morocco and look set to follow suit in Egypt, though militant Islamists have so far failed to take advantage of the chaos.