"In the UK you also risk having the vehicle confiscated, and then offered back to you at market value, on top of a fine etc. It is cheaper to murder someone in the UK than deny the greedy government some money. Oh, and people have been caught using veggie oil in the UK."
This seems to contradict what I have read elsewhere here which suuggests that the only action taken would be that you have to pay the duty on what you have in the tank.