Roughcaster - didn't see your message before I went home last night so I went for the plaster repair stuff!
I mixed it fairly thin and smooth and it seems to have done the job really well. I'll sand and paint it tonight, but so far it looks OK.
Thanks for the advice, I'd have been buying...
We have removed a self-adhesive border from my son's room and it has taken the paint with it in many places, so there are now 'steps' in the old paintwork which will obviously show if we paint over. Is the only solution to sand? We don't want to use another border, just plain paint.
If...