Done Madame Tussauds? Visited every gallery in the British Museum twice? Sailed into the sky on the London Eye and seen the capital spread out before you like a Google Street Map? Soon you will have something new to divert you on a wet Bank Holiday. Boris Johnson, the Mayor of London, wants to turn Scotland Yard's Black Museum into a tourist attraction.

What does it contain? Exhibits relating to investigations into Jack the Ripper, Dr Crippen and the Krays. Also hangmen's nooses, death masks, blood-stained weapons, that sort of thing.

As if foreigners didn't have enough reason to think twice about moving to London - what with the wilting economy, and weather so unpredictable that it makes England's cricket team seem a model of steadfast consistency, and the arrival next year of 50 per cent tax rates - visitors will now be able to glimpse a side of England almost as scary as Damian McBride's e-mails.

Why suddenly reveal this pitch-black side of Britain now, after its being kept for 135 years behind doors that were unlocked only for rare visits from police officers and ghoulish-minded celebrities? Maybe the mayor thinks that by reminding us just how bleak life can really get, it will take our minds off fears that the nation's GDP, on current trends, will by mid-2010 have sunk to roughly the same value as a Kit Kat. It's a bit like the theory that to take your mind off a searing headache you should wear tight shoes.

His aim is nobler than that. The mayor wants the new museum to celebrate our emergency services. They deserve celebrating. And we? We deserve to be allowed a freer peek at a world that, however macabre, colours the country we live in.