To answer my own question..... Yes they do come off. Take the wheel off and pull. Simples.
Not sure if I like them or not now :/ I've put them back on (to be honest because it looked like rain and I couldn't be arsed to take the other 3 wheels off and do them too. I'll wait for a warm sunny day and hope my enthusiasm returns.....
So that'll be some time in 2015 then proxy weather!
Had to replace an alloy wheel, the new wheel came complete with a set of dark grey inserts which are attached to the rear of the wheel with 4 screws per insert. I now have a spare wheel but there is nowhere to put it