I'm still not sure about this. In one respect it seems like a great idea - hopefully it would result in criminals actually being caught (only to get a cushy jail sentence probably, but that's another story). As already mentioned on this thread - the normal law abiding citizen shouldn't have anything to worry about. I think the idea of an ID card is slightly better than the DNA thing.
However, Hamish you do make some very good points. ID theft is bad enough these days, my partner has experienced this down in Edinburgh and it ain't pretty. The thought of someone using your DNA to steal your identity is just frightening. If the government can lose all the data it has in the last couple of months I would hate for them to lose information related to a DNA database. THAT'S scary biscuits.