Listening to R4 yesterday, discussing how a crim was convicted on DNA evidence.

The forensic scientist mentioned in passing that the results obtained in this case were matched against a database of 3 MILLION samples.

As far as I am aware, the law still requires the police subsequently to destroy samples that have been given during enquiries.

Since the scientists and lawyers routinely get the probabilities wrong in court - it's a conditional probability calculation (see Monty Hall problem elsewhere) - suggesting millions or billions to one probability of bang-to-rights against the defendant whereas in fact it's far lower - I'm not sure I'd volunteer my DNA if requested.

The police were supposed to do the same thing for fingerprints - destroy print records except for unsolveds and those of persons convicted - but they never did.