Customs have always scared me as have VOSA.
Years ago my mates dad was using red in an old escort diesel. Now these things sounded like tractors at the best of times.
He went on holiday to Spain and, as I’d been doing some work on the car for him, he allowed me to use it as it was better on fuel than my car.
I knew he was running on red but stupidly started pottering round in it. Went to blackpool and they were pulling all the taxis and vans in on the prom and customs were there. I panicked and turned the engine off and rolled past them so they couldn’t hear it was a diesel 😯 😳
Got away with it but took it as a warning and parked the thing up and never touched it again.