Don't talk to me about back brakes. Couple of years ago I took my bird to a P&D motorcycle for an MOT and they failed it on the back break. Took it away disassembled the caliper, gave it a deep clean and fitted new pads. It still failed. They said it was probably this bit ere that had failed and would cost a fortune to replace. Spoke to John about de-linking the brakes and he went off on one about incompetent arseholes. The upshot of which was, I took the bike to a different garage (Jumbo Breakers) and they passed it with flying colours. They even offered to back me for a complaint against P&D to VOSA though I couldn't be arsed with all the hassle. Needless to say, I've not set foot in P&D since.
The tester I used had a special custom made tool he used when testing linked brakes on the rollers at Mot time...a,ruddy great lump of 4x4 they he used to trick the measuring system if my Bird looked like failing on the rear brake.
Sometimes common sense is better than the rule book.