The MoT is a test of roadworthiness, not conformity. So long as the lights give the right pattern, they should pass.
Only the police, or possibly VOSA can get you into trouble regarding conformity. For example, if you have a car with wheels that protrude beyond the bodywork, it can still pass an MoT, aside from a possibly advisory, there is little the MoT tester can do about it. He can't fail you unless there is a specific mechanical fault. The police on the other hand can pull you over and serve a notice to get it fixed (which bizarrely probably has to be stamped by an MoT station!).