This is going to be a pretty short post as there isn't much to add to this discussion other than what is said in these two reports: first Ben Goldacre on the bad evidence used to justify long term retention (ie 24 years retetion) of DNA data taken from those who are arrested but not convicted or cautioned. Second is this article by Charles Stross on the odds of being a false positive in a government database check (in this case CRB check and why he doesn't give school readings of his books).
The only thing really that I want to add to the debate on a database of our DNA etc run by the government is that the risk in terms of security of a database that will ultimately link ALL your information in one place if breached is pretty horrible. I'll briefly expand this: the DNA database would be likely allowed to expand (through ID cards etc) to cover everyone and be multi-use, ie your medical history would be there you NI number what ever. Even if this doesn't happen a single source of information would make identity theft a utterly crippling crime, especially as it would be most likely a random person who would be used to act as a patsy for someone else. Although this is less likely given the current technological state it is likely only a matter of time before the current DNA system starts leaking.