Hi Keith Jim here, firstly scrape off all the flaking plaster, then get yourself a bucket , half fill it with water , add one cup off vinager to the water and coat the walls all over , this will kill the alkali in the plaster which is causing the paint to peal off , then go to a builders merchant and buy some P.V.A. sealer , when dry should be ok to repaint walls, but allow the vinager to dry first before going over with P.V.A. sealer, sounds odd i know but been painting and decorating for over 30 years these are tricks of the trade , hope this helps.
jim
January 2010