I think the term Gordon Brown uses is "Rebated fuel oil" One of the main problems has been use by road hauliers and Taxis of the red diesel and organised crime washing the dye out of red diesel by using acids.

The washed stuff rots any alloy parts in the fuel system, but all machinery runs better on the red than it does on the taxed white due to all the cleaner aditives in the latter.

There are lots of random checks on road users here in North Yorkshire, but I have read about fishing boats having their fuel checked at Stornoway in a customs swoop, and I can't understand why? Is it because cheaper fuel still is available from abroad? Is this the yellow diesel?