Ugh, it looks like the solenoid is gone, not looking forward to pricing a new one. I got it open in the end thanks to a cached google post. Basically there's no easy access release, you need to take off the interior panel that the right rear seat belt feeds through. it is the white one and comes off easily.
the text is below, I will attach some pics too.
"This happened to our 55 plate clio this weekend. And I felt compelled to join this forum to post a bit of useful/accurate "how to" information.
On our model, it a regular bog standard clio, there is no emergency release pulley or clip despite what the previous posts say. I phoned the renault dealership that sold us the car and they confirmed this.
It is possible however, as I discovered eventually, to squeeze ones hand onto a tiny element of the central locking solenoid that locks the fuel tank door if you unclip the trim around the rear A frame where the fuel door is situated.
On our clio (with the trim removed) we seem to have an airbag unit just the above the seat belt unit. To the right and very slightly up from the airbag gas canister it is possible to get ones hand in to a small gap (this will be directly above the fuel door. Here you can feel what seems to be the top of a small piston or plunger. This is the lock device for the fuel door which you can pull up. This should "manually release the fuel door and you can fill up and then sort the route cause of the problem.
DO NOT attempt to tear off the door, there is no way for it to come off without causing major damage despite what you may think.
Hope this helps
Vaz"