As above every so often when I get out after a drive its popped open

sounds like a short somewhere...

The most likely cause is a faulty switch. The motor has a constant +ve and the switch connects the other end to ground. A short to ground on the blue/red wire between the switch and the fuel flap motor is less likely but a possibility.

Is the release button catching on the radio?

I thought I would have heard it open and wondered if the catch was slack?!?!?

However they are good ideas! Ill put a meter on it tomorrow

I was going to suggest that maybe the catch was only just holding it in place, and on a warm day maybe it released...?  Otherwise dodgy wiring.

And it was the release button catching on radio