I was going to add this as book of the month in brainmail, but I figured it was a little depressing. Here is fine, of course! One for the scenario thinkers at the Ministry of Defence and MI5 perhaps?
A State of Fear: Britain after a Dirty Bomb by Joseph Clyde.
Joseph Clyde is a pseudonym of George Walden btw, a former diplomat and government minister. The book is a novel
Amazon link here.