The announcement came after a meeting of the government emergencies committee Cobra, following a burning car being driven into a Glasgow airport terminal.
The BBC has just said that one of the men in the car was carrying "a device" which would, they believe, link this attack to the attacks in London.
Possibly even more frightening is that these attacks may not be linked to known terrorism organizations, fueling theories that new, unidentified groups may be out there, according to analysts working in the UK. In other words, groups for which there is no intelligence whatsoever, nothing to rely on.
More at the Washington Post.