As I understand it you have to drive direct from your point of departure to the MOT station, you cannot go shopping on the way. Stopping for petrol is probably acceptable.
This isn’t true. I read a story about a guy who went to court rather than accept a ticket. He stopped at a shop to buy cigs, police pass and try to do him for no MOT.
When it gets to court, the judge ruled that it was a reasonable reason to stop.