Found this just now whilst trying to understand the emmission tests - quite an informative site actually The MOT Test A few things to note to help clear any confusion up of topics I have seen in here: DPF REMOVAL: From February 2014 the inspection of the exhaust system carried out during the MOT test will include a check for the presence of a DPF. A missing DPF, where one was fitted when the vehicle was built, will result in an MOT failure. A vehicle might still pass the MOT visible smoke emissions test, which is primarily intended to identify vehicles that are in a very poor state of repair, whilst emitting illegal and harmful levels of fine exhaust particulate. It is an offence under the Road vehicles (Construction and Use) Regulations (Regulation 61a(3))1 to use a vehicle which has been modified in such a way that it no longer complies with the air pollutant emissions standards it was designed to meet. Removal of a DPF will almost invariably contravene these requirements, making the vehicle illegal for road use. The potential penalties for failing to comply with Regulation 61a are fines of up to £1,000 for a car or £2,500 for a light goods vehicle. HID LIGHTS: HID headlights can cause dazzle if they are dirty or aimed too high, so they are generally (if light output exceeds 2000 lumens) fitted in conjunction with headlamp cleaning and levelling systems. Where HID or LED dipped beam headlamps are fitted the tester will switch on the headlamps and check the operation of any headlamp levelling and cleaning devices fitted. The car will fail if a headlamp levelling or cleaning device is inoperative or otherwise obviously defective. If a headlamp bulb is not seated correctly the resulting beam pattern will be indistinct and this will result in a test fail. Might be a nice idea to keep a running tally of those commonly asked MOT questions in one thread so that anyone looking can see all the answers in one go.