Mission accomplished. Winfixer was simple to remove using the VundoFix tool downloaded from the internet. Autopatcher took 20 minutes to download and a further 20 minutes to bring the machine up to date. There was a single (worryingly slow) re-boot but all was well afterwards. I managed to revive Norton's and get that updated too. It's now working on autoprotect again and I left it happily scanning away. Thanks once again for your invaluable help Mac.