Hi Dustypuss,
Many years ago I bought a bungalow with one bedroom having three outside walls. I had problems in this particular bedroom with condensation. Our wardrobes were always damp and the walls behind them blackened.
I called in Rentokill to see if they could solve the problem. They suggested "Cavity Wall Insullation", and guaranteed that if it did not solve my problem they would refund my money and carry out any other work free of charge to remedy the dampness.
They drilled a series of holes in the walls and filled the cavity with "Rockwool"
My dampness was cured immediately, My heating bills were reduced overnight and both my wife and I were the happiest couple in the street.
In my opinion it was well worth the money.
Regards.