Are you paying highway fuel tax?
Yes, road tax is charged on all "clear" (ie, on-road) diesel fuel. There is clear #1 diesel available in the fuel chain. You might have to ask your fuel jobber for it, but it is available, road tax and all.
For our on-farm fuel, it is dyed, aka "red" fuel, and that doesn't have road tax on it.
For those who might be thinking about running red fuel in your diesel automobile, ala the late 70's and people running heating oil in their diesel cars: don't. Don't go there. If they dip your tank and find traces of red dye, you don't pay road tax on the fuel in your tank. Oh, no. You pay road tax, plus a penalty, on the size of your storage tank. For us here on this farm, that's 4,000 gallons. Doesn't matter how much fuel you actually have, how much you've actually used without paying road tax. They have the regulation worded and enforced in such a way as to maximize the pain.
So, here's a tip from someone who has read the regulation: don't do it. Paying the road tax is much cheaper.