6 months ago just before we moved into our new (25 year old) house, we had everything professionally painted. Only a few months later I noticed the ceiling in the lounge was turning blotchy brown in places and now, six months later the whole ceiling in that room is extremely discoloured. You can see the outline of the beams clearly as the ceiling is still relatively white where the beams are. I thought perhaps the previous owners were smokers but have since learned this is not the case. Now the problem is spreading to most of the other rooms in the house, rooms that are nowhere near the lounge. two of the bedrooms are also very bad. Its pretty upsetting as the paint job cost us a fortune and I am reluctant to re-paint myself until I know what is causing the problem! Any ideas anyone?

Unfortunately it sounds like you have a problem with damp in your roof space. sounds like rain is getting in causing the discolouration.