Ooo, got to admot this is news to me. Our force certainly hasn't got this idea on the go at the moment. It used to be if you were charged with an offence, your DNA & prints were taken. The police can now take these before charge.
I haven't checked out whether this applies to your situation, but if you went to court and were aquitted, you could demand destruction of your prints & DNA, and could even pop allong to witness it.
This new practice is probably being brought in through criminals giving false details whilst they are being issued a HORT 1 (production of documents slip).
It is not uncommon for criminals to give details of another person they know (and who looks similar). I once had a guy give me his brothers details, he did this because he was disqualified, and didn't want to be arrested. Unfortunately he hadn't spoke to his brother for a while, and when his brothers details came back over my radio, he was also disqualified

I later found out who he was in custody, and also charged him for obstruct police
It should be remebered, that if the officer who stops you is not satisfied that he has your correct name, address and date of birth, he can arrest you under secion 25 of PACE, and take you to a police station. At the station your dentention would be authorised untill your identification was confirmed.
I understand your concern of this practice, and would check as to whether your print will be destroyed upon prodution of your documents.