Security services estimate that about 2,000 Islamists based in Britain “are actively planning terrorist activity of some kind.”

The warning comes as Britain begins preparations for next year’s 2012 Olympic Games, which has been described by intelligence agency MI5 as the biggest security operation in the country’s history.

Six men from Birmingham were arrested two weeks ago over an alleged suicide bombing plot which Lawfare Blog termed “homegrown-but-trained-abroad.” Two of these six, Irfan Nasser and Irfan Khalid, allegedly traveled to Pakistan to train, made “martyrdom videos,” and planned to carry out a bombing campaign.