This is tricky!! took me a while to get mine off, (as you cant buy them anymore) soaked it in weasle **** (wd40)) a few times, the outer ring acts as a clip and is exposed to the inside wheelarch and gets covered in mud and crap, so blew the crud out and scraped it off (with high pressure air line) more wd40, and you have to gently tease it off by pressing the little tabs at the back and levering the ring, i used a plastic spreader ( or credit card) to jam under the ring, (oohh!!) to protect the paint and a mini screwdriver, and a plastic trim tool, took me a while and wound me up a bit but had to come off as holds the filler neck in, but perseverance will win!! Ant!