The place that used to MOT my Rover 25 worked an MOT fiddle. If I asked them to do anything, say replace tyres that were down to near 2 or 3mm (with high mileage each week, they'd soon be gone or punctured) or replace the back box, they'd record an MOT fail, do the job & retest. It didn't matter to me as the car was sold for spares at 176k miles & 14 years.
Interestingly,I was pulled over for a VOSA/Police check near Nottingham the day before my MOT & the only thing they queried was some bad rust on the entry pipe to the the back box. They were happy when I showed them my MOT was booked & I had the receipt for the new silencer they'd bought in for me. Sure enough, the car failed on the exhaust & passed an hour later!