The M.o.T. station is in fact a garage which sells and fits tyres. After the vehicle has failed its M.o.T. on a bald tyre, the owner asks the proprietor of the premises to fit a new replacement. The proprietor does so, but by this time it's 5 pm and he wants to close up earlier than usual because he's shagging his blonde receptionist and wants some fun with her in his office prior to driving home before his wife gets suspicious. Consequently, there's no time for another M.o.T. on that day.
As the car owner drives off, the proprietor's wife speeds on to the premises with a squeal of tyres and leaps out of her car carrying a double-barrelled shotgun. She marches into the office, from which two loud bangs are heard.
The car owner drives away, happy that, legally, he or she still has three weeks to get his vehicle tested. However, this won't be possible in the foreseeable future at the garage that previously failed the car as it will shortly be sealed off by the police as a scene-of-crime.
Sorry - got carried away there.