I have been looking online and a major cause of damp in some houses is closing up fireplaces. I think this is definitely the case with the dining room section fireplace. It did have a vent but it was painted over so this has been removed today to let some air through.
We haven't decided whether to open this fireplace up but we think we might open the front fireplace (in the lounge section). It will be too much of a big job at this stage to have a proper fire but at least we can have a nice fireplace.
Nathan is still preparing the wall in the front bedroom and painting it with a base coat, hopefully at the weekend we can move onto some colour. We think we might be able to sort out the floorboards and leave them on show but we have not looked into this much yet.