If the London police have apprehended a member of the current active terrorist cell for questioning, then the leaders of that cell know their time is short; their preparation and recruiting are a rapidly wasting asset. Their logical response is to immediately launch any attacks they can. It seems that just this might be happening; a bomb carrier was shot at Stockwell station this morning, and Moorgate has just been evacuated. I expect the next few days to see a continuation of this, as the leaders rush to "spend" their recruits. Batten down, mates.