I can't advise on possible causes, but have you thought about getting a dehumidifier in?

I once had a property in a block of flats we managed that suffered with a damp wall originally caused by a faulty lead gulley, the gulley was fixed and the upstairs flat walls dried out, the downstairs flat stayed damp (and was still damp) 12 months later.

We spent ages trying to trace what was causing this damp, until a damp contractor (correctly) advised us to get a dehumidifier in, turned out as the wall have very little ventilation on the external side the wall was never actually able to breath and dry out naturally.

The dehumidifier pumped out an unbelievable amount of moisture (over the space of a week or so) and now the wall (and flat) is bone dry.

Thanks so much for your reply, i referred this thread to a Damp surveyor and he said there must be a leak, exactly what the scruff said. I called Thames Water last week and told them my neighbours water meter which is about 6 feet away from the recessed pochway of our home's is full of water. They came and found a leak which they sorted out.

I think what happened was that the water from the meter came through the shuttering under the concrete into my neighbours house. His wall must be sucking up the water and penetrating through to my side. If this aint the case then i think i will shoot myself.

Anyway i will try a heater and a dehumidifier. If not then i will hack the plaster off, replaster with Thistle Drycoat and then multifinish.

Thanks for all your replys.

Also what do you think of water coming in through a leaky meter six foot then being sucked up by a wall? Im not so sure.