Thanks for all your comments
I mentioned the alternator light was on, so that was first on my list of jobs
I changed the external regulator and replaced the brushes but it still wasn't charging so I started to dismantle it further.
The fan and housing were very corroded and it took a lot of careful hammering to remove the pulley, then I removed the 6 through bolts, all the terminal nuts and brush holder so I could split the alternator, leaving just the rear ally case in the fan housing. More careful hammering and it was apart. A close look revealed some rust and a few cracks in the diodes so I ordered a matching exchange unit.
Fan and housing not looking good.
It seemed sensible to clean up the fan and housing while I was in there, and it also meant the new alternator slid into the housing without any effort. I spent a few hours with a wire brush in the grinder and it definitely looks better, although nothing like the standard of some others I've seen, the fan blades are quite pitted in places. Back on the car, everything works as it should, and I refitted the original regulator.
Not knowing the recent history of the car, I also treated her to an oil change, a messy job as there's no drain hole in the sump plate, but I got a total of 11 litres out and refilled with Valvoline VR1 20/50.
My next job is to repair the steering wheel - luckily the leather is not torn, it's just the thread which has rotted, there is no thread at all in this picture of the top half of the wheel. I've got some strong thread and some curved needles so I'll have a go over the weekend...
Gavin