The switch is basically the same as that used on many other cars, not just MG Rover but also Ford and Renault of the same period, and probably others. the switch is of Ford origin originally.
Mirror backs can be swapped easily, even between manual and electric.
All MG Rover with electric mirrors have permanently heated glass, as do manual mk1 MGF mirrors which are manual.
Home to black Alfa Romeo 159 3.2 V6 Q4 ,green MGF VVC and red MG Maestro T16.
MG - the friendly marque.