Vehicles first used on or after 1 January 1971 must be fitted with at least two obligatory stop lamps. Any additional stop lamps fitted and connected must be tested. Can't find any info saying you must have a third brake light, although all modern cars I can think of have one, so maybe cars have to be manufactured with one, but I imagine if you were to remove it, it would pass, but having one present and not operational would be a failure. I'll ask my MOT friend tomorrow!
Yep as I and many others said, asked an MOT tester today.
