I wonder whether there's any soffit venting in the OP's house. Easy enough to fit soffit vents if there isn't.

No-one seems to have mentioned a vapour barrier yet. Surely a relevant consideration too, especially in relation to the bathroom which with all those light fittings is likely to be very leaky.

John

A great big thanks to all who have advised me especially Chris the Builder. I was able to detect a cowboy builder when he came to look at what needed doing and quickly got a second opinion from a much more reputable chap. I do have condensation as diagnosed and new breathable felt is required. I also have issues with the ridge tiles due to weather damage and the felt near the soffits is collapsing due to age etc. I am having the job done by a professional roofer and feel better about the whole situation. If it wasn't for the advice I have had from you all I would have been ripped off and had half a job done.

Thanks Again