Horse for course

I would hope that only "biometrics" (key parameters) of the (e.g.) fingerprints would be held, and not images of the prints themselves; also, protected with a site-specific key.

This would render them of little use to a third party.

I would also not expect the system employed to be configured to allow "trawling" if its express purpose is authentication - "is this person allowed in this area ?"

But then again the Govt. doesn't "need to know" where we have been driving in order to charge for road use, but the proposed schemes all involve recording our movements.