Hi again RED:
I misled you in my initial post by leading you to believe that the Police could not take DNA + fingerprints just because you've been arrested. They can, of course, wrong though that seems.
And presently there's a DNA database with details of many thousands of innocent people on it. Opposition MPs, and some Labour, are campaigning to have that changed, rightly too in my opinion, but until if and when it is, then unfortunately your son's details will remain on it. And even more outrageous is the fact that at present the details remain there for life!
If you're interested, there are websites where you can "sign" a petition to have the Law changed, i.e. the Lib Dems have one such form.