Thanks everyone for all your advice. Looks like it was a combination of things-the pump relay being the starting point. Evil sidestand cut out disconnected, all relays checked and given a little bit of grease. Fuel pressure regulator removed, beaten, sworn at. Put back together, taken to bits again because the black plastic cover for regulator was still lying on workshop floor. More swearing. Lots of kicking and away she went!!! A celebratory gin precluded any test ride but am optimistic that the dirty deed is done.
Thanks so much.