you know you have a mk2 when the poxy central locking packs up and you have zilch petrol and can't get the fuel flap open,arrrrgh!
Behind the carpet in the boot on the drivers side, strip it back until you can see the central locking pump and there should be abit of white string/lace, if you pull that it pulls the pin down that holds the petrol cap shut.
And hopefully it should open. .
Oh and it may be worth pulling it through the vent type holes in the carpet and leaving it there, just incase.