Behind the scenes, there's a lot of procedure in place to ensure that arbitrary government agencies don't have arbitrary access to arbitrary things that "the government" knows. The DVLA has a legitimate basis for collecting information about vehicle registration, and there are often legitimate reasons to pass this information on to law enforcement; but that doesn't generalise to arbitrary information about the occupants of a vehicle. Collecting arbitrary information just in case the police need it is one, seemingly-benign route to a police state.