This is something I've never seen for sale before. I've seen manual ones, but an electric one seems very unusual! Certainly not cheap, but could be a lovely accessory for someone to fit.
http://www.ebay.co.uk/itm/Rover-P6-sunr ... 3a8af4518a
http://www.ebay.co.uk/itm/Rover-P6-sunr ... 3a8af4518a