It worked! He jumped in, shook himself to get rid off the excess water (and, I discovered later, the mud - there are mud spatters all over my car including the ceiling!) and installed himself in the front seat in front of the heaters. I called the council, who sent a lovely, friendly woman to come and pick him up. He was microchipped so they were able to call his family and I'm sure he was safely installed at home very shortly (hopefully a better secured home than the one he was able to escape from!).
Good deed of the day done I drove home (slowly and carefully, of course) and walked inside very pleased by myself. Lucy smelt me, determined that I had been spending time not only with an animal who wasn't her but a dog (!!!!) and peed on my swimming towel while I was in the shower. Stupid, adorable little cat :)