If you are incredibly well informed, persistent and lucky, t is is sometimes possible to get your DNA and other personal data removed from Police databases, after you have been wrongfully arrested etc.
David Mery, a former technology journalist and magazine editor, seems to have eventually managed to do so - see his blog post: Innocents are exceptional
The fact that so few people are removed from the database, (only 115 last year) when they are innocent, is an intolerable scandal.
As explained by David, the system for doing so is a complicated bureaucratic, Kafkaesque nightmare, which is likely to be far beyond the abilities or resources of most of its victims.
Meanwhile, the Daily Mail has found, via a Freedom of information Act request, that a 7 month old baby has had her DNA details put onto the National DNA Database, by the West Yorkshire Police, at the request of the West Midlands Police. This innocent child now faces the prospect of having her DNA profile and possibly DNA tissue samples retained for the rest of her life, for no good, valid or proportionate reason.