I had an AMC Hornet with the gas filler behind the license plate in the middle rear. It was quite convenient as one could pull up to a pump on either side and fill it up.
However, the safety issues/experiences from the 60's to 80's have led to big changes today, mostly for the better, although everyone likes to complain.
The old pickups, of course, had the gas tank behind the seat. Perhaps not so bad, but any leak puts gas in the passenger compartment.
The Land Rover I just got has the gas tank under the passenger seat. I have a feeling it would be under the driver's seat in the UK. No filler neck, so one must raise the seat, open the door, and the hose goes right into the passenger compartment (as well as any spills).
My old Fiat 500 had a "Frunk" with the tank just in front of the cowl. No filler neck, so one opened the trunk, and filled it up. Top it off because there is a difference between a 4 gallon or a 5 gallon fill.
Of course cowl tanks were common on old Model T and other cars, as well as on tractors.
You mentioned missing gas cap. The little plastic gas cap wire is nice. No more lost caps. And, remember to close the cover.