I spoke to an MOT tester. He is aware of this situation but his view is different. If your bulbs do not meet a Standard that is a matter of law not an MOT issue. The MOT'er responsibility is to test the lights, If they function properly they pass, if not they fail. He did say that LED light might fail the light distribution test for the main and dipped beams. This is because the LED is unlikely to have its light source in exactly the same place as the original fitted bulbs and would not function properly in the original reflector.
I have fitted a set of LED bulbs to my bike and find them very satisfactory. It is hard to tell the difference, in light spread, between main and dipped beams. But, I could hardly see a difference between beams with the original bulbs fitted anyway.
I wonder if anyone out there has fitted led bulbs and passed an MOT test?