Fuel tank non-return flap

[Erich Stahler]

Wondered if anyone knows where I can get hold of a fuel tank flap as per below in the UK?

[drmotorsport]

Depends on the car but If you've got a mainstream manufactured car with standard fuel tank and filler pipework from the last 20ish years, then it's probably already got a non return flap built in to the filler socket.