True, you can't directly identify the driver, but I would imagine the correlation between number plate and one or a very small number of individuals who have use of the vehicle is strong enough (in most cases) that it could be regarded as personal information.

You can once the inevitable database leak of driver information details leaks from the DVLA/insurance companies.

It might take a few years, but you can use this dataset in the future to understand who owned the vehicle at this time and reconstruct their movements.

Using collected information it's possible a computer can remember every journey you've ever taken; this car with this reg plate was here at this time at this place, and they did not have a valid tax/insurance at this time, or it could be useful during investigations