None of the stories in the media seem to have any specifics about this alleged plot whatsoever. It may or may not be true that someone was planning to do something unpleasant with this substance, though there are plenty of much nastier and cheaper chemicals that a terrorist could release in the underground or put in a bomb.

What is true, though, is that this story was given to the media in order to frighten the public and make us more receptive to ideas such as compulsory ID cards. That connection is almost too explicit on this occasion: as soon as the story had been placed in the press, Blunkett was using it to back up his own position.

Remember also the tanks around Heathrow just before the start of the Iraq war and the North London ricin case (still no-one has been charged). The government can use the threat of terrorism to manipulate public opinion at will.

(Note: I'm not saying that there is no threat.)