MACK said:
I know when a lot of MOT tester's see a car and know its actually got HID's retrofitted they "play dumb" on this. Most notice the difference if it a decent kit giving decent light but don't think its a big deal. Unless you get a real stickler for the rules you'll probably be fine. One thing I will say is if it does fail its could be awkward taking it to another station "around the corner" and playing dumb. As soon as they enter your cars details on the system they have access to previous MOT history/fails etc so might see what your doing. Then again they might not be bothered anyway!
I'm not sure they play dumb per se - I know from the output when a lamp has HIDs fitted, so expect testers to know too, but as they can't dismantle to prove and the manual says to give the benefit of the doubt for the washers and levellers, believe that's what they do. If the beam was all over the place it would defo fail - think a Barry boy Corsa with reflector lenses.