Well unless the rules have changed the time spent (self) positioning would count as part of the Flight Duty Period, assuming flying duty was to follow at the end of the road journey.
I suppose it would also depend on the contract between the company and the employee as to whether the company can "order" a crew member to self position by road.
In the past some companies have treated self positioning as a sector the purpose of max FDP allowed etc.
There is also an insurance aspect as you are not using your car for "social, domestic and pleasure" and therefore in all probability you won't be covered on your own insurance in the event of a claim.
My own view is that crew members should not be required to drive themselves prior to duty since road conditions these days in the UK are not conducice to one arriving in the right frame of mind prior to going on duty. The company ought to provide taxis, etc. but I aware that some companies do expect their crews to self position from time to time.
I also imagine that it is the case that having landed back at said airport the crew member then has to drive back home/base again at a time when they may not be in a fit state to drive a motor car as a result of a (lengthy) duty day. I know at least two of my colleagues who have woken up in hospital after they have dropped off to sleep at the wheel although they both lived relatively close to the airport - not very good economy for the company if they are off sick as a result!