Unimog Club UK

Go here
https://www.dvla.gov.uk/dvla/forms/onlineleaflets.aspx
and click on V355/1 this is near the bottom of the page.

Once you have downloaded the form read section 11 and 11.1 on page 7 which gives details of the taxation class and limitations of use.

There is no minimum speed limit on UK motorways but you can be charged with dangerous driving if you are driving to slow which can cause a hazard to other drivers.

When I bought my 406 from London and headed for the M25, I realised that I had made a huge mistake. When I gave the vehicle full throttle in top gear I was only able to achieve 40mph according to my sat nav (very worn throttle linkage which is now fixed) I had artics shooting past me like I was stood still and I couldn't wait to get to the first exit to get off. I also believe that a tractor according to the info above should not be used on the motorway at all.

Make sure that if you are on the road that you are using your vehicle for one of the reasons listed. If not the hand of the law will come down on you.

I hope this helps.