Thanks for all your helpful suggestions, and you too Ben.
So the paintings done, well the ceiling and walls in all the downstairs, up the stairs and on the landing. Quite a job, 3 days work from morning to night.
I looked at the magic paint that goes from pink to white, but they didn't do it in the "right" white. Any budding chemists, do you know the additive, something that's pink when wet and colourless when dry, yet is soluble won't effect the properties of the paint?
I went with a system of filling the roller and painting a strip, then spreading that out by rolling perpendicular to the 1st strip. Then re-filling and painting another strip overlapping the previous and spreading again. And repeat and repeat and repeat... I have still ended up with patches! Can I just cover those bits or do I need to do the whole ceiling again?