Start by ventilating it well. Add powerful extractors to bathrooms and kitchen.
I am concerned that you had rotten skirting and "damp course done."
I suspect this means chemical injection which will not have repaired the source of water.
You do not mention the age of the house but it is unlikely to have been built without a slate damp proof course. Slate does not wear out and lasts for hundreds of millions of years.
So there is a defect.
Common ones are:
DPC bridged by ground level being raised since the house was built, usually by additional paving but sometimes by render or a cement plinth
Water dripping from gutters and downpipe (if these have been repaired, the wall will dry out in about a year)
Broken clay gullies and drains (IME clay gullies in old houses are always cracked and leaking, though I am told there are some that aren't)
Old water pipe leaking under the floor (iron pipes leak after about 50 years, lead pipes after about 100 years)
You will be able to see where the drains are.
The water supply pipe is pretty sure to run in a straight line between the outside stopcock (probably where the front gate used to be when the house was built) and the inside stopcock ( where the sink used to be when the house was built).