A much-needed public debate about covert surveillance has begun, thanks to the allegation that counter-terrorism police officers secretly recorded discussions between the Tooting MP, Sadiq Khan, and a constituent, Babar Ahmad. Mr Khan was visiting Mr Ahmad in Woodhill Prison in Milton Keynes, where his constituent is awaiting extradition to the US on charges of supporting terrorism. If their conversation was recorded, this was a breach of the so-called "Wilson Doctrine" which forbids the secret surveillance of MPs without explicit ministerial approval.
So was it a cock-up or a conspiracy? The decision was apparently taken by a Thames Valley Police officer. It is unclear at what level it was authorised. It is also unclear whether the police knew it was not permitted to bug an MP. The Home Secretary, Jack Straw, has promised a swift inquiry into the affair and has pledged to root out any abuses.
It is reasonable for MPs to expect confidentiality when dealing with constituents, in the same way that doctors, lawyers and priests require an understanding of privacy to perform their jobs properly. Without an understanding of confidentiality, why would constituents with a sensitive problem approach their political representative?
But this is not a matter that concerns only the privacy of MPs. The Interception Communications Commissioner, Sir Paul Kennedy, highlighted how state surveillance has become routine in Britain when he reported last week that more than 250,000 requests for private communications were made in 2006. The Home Office also issued 1,333 warrants to authorise bugging operations in that time.
And eavesdropping is no longer just carried out by GCHQ and MI5. As this case shows, the police are bugging too. And a far wider pool of public institutions now has access to our communications records. Almost 800 public bodies, from Revenue and Customs to the Food Standards Agency, are now permitted to request communication intercepts, as well as emails, records of telephone calls and post.
Secret surveillance is obviously necessary in counter-terrorism and organised crime operations. Indeed, there is a powerful argument for surveillance transcripts to be made admissible as evidence in court to increase the number of convictions. But the proliferation of eavesdropping and secret information gathering has taken on a sinister momentum of its own. This is part of a trend that has seen Britain acquire more CCTV cameras than anywhere in the world and brought us the prospect of biometric ID cards. If anything good can come out of this row, it will be that we wake up to the casual and dangerous erosion of our privacy.