nope, remaps will not become illegal, there was talks about having your car chiped being an MOT failure, not sure whats happening with that, so if you simply have a piggyback remap box that plugs into your ecu and fools the car into overfueling and over boosting it will fail, however if you have a proper remap (i.e. the settings and program on the ecu reprogramed) it will not fail.