It's not often you ask a question which completely silences some of Britain's leading minds on security.

But it happened this week at a briefing by Olympic security chiefs from the Met Police, Home Office and 2012.

Why, I asked, were there clauses in the Olympic Act which allow the police to raid the homes of people with anti-2012 posters in their front windows?

Chris Allison, the man in charge of the Games at the Met Police, had just told me that the police would not be using the powers in the Act to do this.