Looking a little closer it does seem like it could be a photoshop, although a very convincing one - two things that would back that up:
1 - If you found an unusual, clearly bespoke 1970s GT car abandoned somewhere you would surely take multiple photographs of it from every angle, or at the very least one showing the rear aspect as well?
2 - The registration is not on the DVLA database. There are many reasons for this to happen so can never be proof of anything, but the most likely being that the car was off the road and untaxed at the time the DVLA moved over to a computerised database in 1983 and has never been on the road since, which would mean this was only on the road for 5/6 years. If it really is what it appears to be - a professionally made bespoke high-end GT car, this seems unlikely to me.
Again, not proof of anything, but something to think about at least