Thanks for the advice.

There is a bit of 'emulsion' on the dipstick but nothing much else to
see.

Since I posted the message & the coolant was topped up, there has
been no overheating at all. Before that, the needle went over to the
red on a couple of occasions. The engine cooled down again when I
kept the heater on full, though this varied a bit depending on
whether the road was up or down hill! Don't think it ever
overheated badly.

I've now taken it to another garage for an MOT to see whether any
other work was neeeded & to decide whether to keep or scrap the car.
The mechanic there says he cannot find any problem with the
engine/cooling system! Don't know how thoroughly he has checked it,
but he says its fine. Just needs new front brake calipers to pass
the MOT.

So I think I will just keep running it for the time being.

Out of interest, if there is a small head gasket 'leak', can I just
keep running it & ignore it until the engine finally gives up??

Cheers
Steve