Yes the motor was designed for another application, and if memory serves me correct, it was a light weight industrial cleaner motor and was made by pPolymotor in Italy and was originally designed for 24 and 36 volts, but to keep the weight down on the C5 it was revamped by Polymotor for 12v using existing bits, the 12v was important to Sinclair, as they wanted to run on 12v and 1 battery which was 45Kg to fall within the law, or 60 Kg with 2 batteries.
An interesting link is this one...
http://www.solarnavigator.net/inventors/sir_clive_sinclair.htmand a very old site with the posting of the death throes of the C5 is this one...
http://www.crashonline.org.uk/19/sinclar5.htmeither way, i know the laws have changed, but i feel if the C5 had been launched now, with all of the legal battery vehicles on the road, and acceptance of them, i think they would be a hit