Hi Simon
Welcome to the club.
Watch out for mogs, they get into the blood and can become addictive 😊. If in doubt I'd run it on white especially if ur not in any kind of arb/hortic industry.
With regards to the historic vehicle taxation, it's just a simple form u fill in saying it falls into one of the categories ie agricultural and sign it. I couldn't do it on line so had to go into the post office.
If your In engineering how about a 406 with hiab.... class it as a crane?? And I think they can run on red but dont quote me on that lol
Cheers
Casto