On this red Diesel topic (which, with the derogation of marine red, may soon become harder to buy from a pump);
There is no reason why, if a vehicle is solely used off the highway (trailered to and from events) you cannot use red diesel (gas oil) because the only tax not applied is the road duty. You are free to use red in plant that remaines on site, builders will often use red on diggers and things that get transported site to site.
C&E can only dip your tanks if they have stong suspicion or proof that the vehicle has been on the road ( Chieftan owners can sleep easy then ;-))
However there does seem to be a 'get out' of sorts;
As we experienced during the big fuel crisis about 5 years ago some folks at work could only get red diesel to run their cars, so a phone call to the bods at Customs house revealed that if they popped along with a reciept for how much red they had filled with, they could pay the road duty over the counter and were then issued with a reciept to prove it if stopped,they take your milage and assume a distance by which you should have used it by (but how many tracked vehicles have odometers :dunno:)