Regardless of what the MOT says, its illegal to use HID's on the UK roads without European type approval. The MOT test is NOT legislation, and does NOT ensure your vehicle is legal to use on the road, its simply a safety test which hopefully ensures cars meet a minimum standard.
There is NO provision in the Road Vehicle construction and use regulations to permit HID's to be used on UK roads. Manufacturers get away with it, because they aquire whole vehicle EU type approval, which then overrides the construction and use regulations.
The DFT released a statement a few years ago on retrofitting HID's which basically says, retrofitting halogen headlamps (regardless of type) is illegal. You can retrofit your CAR with HID's however you need to meet the requirements of the original EU type approval issued, which in the case of an A3, means you need proper S3 headlamps, automatic headlamp levelling and headlamp washers.
The DfT document is here:
http://assets.dft.gov.uk/publications/dft-information-sheets/aftermarket-hid-headlamps.pdf
Now sure, nail them in and you'll happily pass MOT's for all time, but have a serious incident which results in the car being properly analysed by the police, and those lights
could be enough to see you in jail. Thats the difference between passing MOT's, and having a road legal car.