Re: I have said it before, I will say it again
"the UK police are not allowed to keep your DNA on file forever"
Alas the articles below do not exactly give one much confidence that the rules are being followed, either in spirit or letter:
http://www.theregister.co.uk/2016/04/05/home_office_settlements/
http://www.theregister.co.uk/2016/03/15/british_police_broke_law_illegal_biometrics_investigate_crimes/
http://www.theregister.co.uk/2016/03/11/home_office_warned_over_police_facial_recognition_abuses/
I can actually see some value to the public in the police being allowed to keep some data, subject to appropriate rules (not necessarily the ones currently in place) and oversight, but if even they are prepared to break the law then there's not really much left to have faith in.