It's 18 mm Goryl, a size often not included in spanner sets. It's possible to make one, see this link
David,Thanks Guys, your kind words are much appreciated! It is a two way street though. Most of the upgrades and improvements that have been made to Wisper bikes over the last four or five years have originated from comments made by Pedelec Forum members. I seriously appreciate the input.
I can't see a problem with retro fitting a connector into the motor cable. If you are a deb hand with a soldering iron it would only take half an hour or so.
Best regards
David