The scientist who pioneered DNA fingerprinting has warned of the increasing danger of false positives as the use of the technique becomes more widespread. Although the theoretical chance of a false ID remains very small, geneticist Sir Alec Jeffreys suggests switching from use of ten markers per person to 15 or 16 would reduce the chance of a false match to around one in a trillion.

Jeffreys, speaking at a briefing marking the 20th anniversary of DNA fingerprinting at Leicester University yesterday, also expressed doubts about current UK policy on DNA record retention. Suspects have their DNA recorded, but for several years now the police have been allowed to retain the DNA profile whether or not the suspect is subsequently charged or convicted. This make it a lot easier for them to grow their National DNA database, and indeed here we find the Home Office salivating over bigger and better DNA retention when it passed the two million mark last year.

Jeffreys' concern is that in some parts of the country retention will lead to an overrepresentation of certain ethnic groups. His solution is either for the DNA data to be destroyed if a suspect is cleared, or to extend the database to include everyone in the UK. We fear the Home Office will greet his words with enthusiasm. No prizes for guessing which option it's going to like. ®

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