LONDON - British counter-terrorism police are struggling with "exceptionally high" numbers of investigations and discovering several plots a year, their chief said on Friday.
"So far this year we have made 218 arrests and are running exceptionally high numbers of counter-terrorism investigations, the likes of which we have not seen for several years," said Mark Rowley, national policing lead for counter terrorism.
"We are disrupting several attack plots a year." Police arrested several people this month in what they said was a "significant" plot.
Britain raised its terror threat level to "severe" from "moderate" in August, and the government has expressed concern that British-born jihadists who have travelled to Iraq and Syria could pose a threat if they return.
Rowley said that extremist groups are using social media in increasingly sophisticated ways, and that police remove over 1,000 pieces of extremist material from the internet each week.
"The growing problem of young, impressionable, and in some cases vulnerable, individuals being radicalised online is an increasing risk," Rowley said.
Much of the material relates to Iraq and Syria and some relates to beheadings, suicide and torture, Rowley said.
In all, 66 people have been reported missing to police are feared to have travelled to Syria, according to the police chief.