Re: @Martin Summers
"Putting it on fuel has its problems. Apart from pushing the price up and encouraging further fuel cleansing to avoid tax - you'd be amazed how people come down to my remote farm to try and steal red diesel for just that purpose. Also smuggling is easy - most foreign truckers coming to this country have extra large tanks already to avoid having to re-fuel here and any excess can often be bought from returning truckers."
I think that's always going to happen though Tom regardless. It's not something most people will do casually and so as a scheme it's less risk and likely to stop evaders. If they're avoiding paying road tax now they're going to keep doing it regardless of how it's collected.