As far as I'm aware for hid to be legal they need to have washer units and also have to have correct lense type so they can't be used in normal lamps, I suppose after iva it woudnt matter. You can however buy projector style lights which use normal H1 bulbs . There's a bit of info here ...
http://www.dft.gov.uk/pgr/roadsafety/drs/hidheadlamps