Kevin Brady wrote:
If anyone else has other suggestions, I would be very happy to read them - I
was planning on using a sharp trowel and polyfilla in the pitted areas, but
I know this can be a bugger to sand off if you overdo it.

Might be worth trying Polyskim? It's a Polycell product (surprise,
surprise) rather like Polyfilla and supplied in tubs of ready-mixed at a
high price - any pro will sneer at it, but I've had pretty good results
out of it under conditions such as you describe. One advantage of
Polyskim is that it goes off very slowly, so you have plenty of time to
prat about and get it flat.

Maybe others have experience with it?

David