http://www.direct.gov.uk/en/Motoring...le/DG_10014246
You will need the new shell plus two major components from the original vehicle. Make sure you have proof otherwise it WILL go on a Q plate.
In order to retain the original registration mark:
cars must use:
The original unmodified chassis or unaltered bodyshell (i.e. body and chassis as one unit - monocoque); or a new chassis or monocoque bodyshell of the same specification as the original supported by evidence from the dealer or manufacturer (e.g. receipt).
And two other major components from the original vehicle - ie suspension (front & back); steering assembly; axles (both); transmission or engine.
Hope this helps...