A Metro 6R4 ! In full 1985-86 rally livery, but the 1983 Y-plate is strange, since the first prototype made its first appearance in 1984, with a launch date set for the next year.

DEJ 810Y

Vehicle make MG
Date of first registration 01 April 1983
Year of manufacture 1983
Cylinder capacity (cc) 2098cc
Vehicle colour WHITE

Doesn't seem to be a re-registration either.

http://www.aronline.co.uk/blogs/cars/austin/metro-austin/mg-metro-6r4/