Incredible - you are spot on! Many thanks for that, you've put an end to two weeks of hunting.

Funny how the main dealers never know this kind of thing.

The fuse was ok, but the relay does rattle when shaken, which I'm sure is a bad sign. Although it does check out ok with a multimeter and 12v applied to it. Still, it's a cheaper thing to try replacing first than the ECU.

I owe you a beer (or ten).