We have a damp patch in our guest bedroom, that is in the middle of the junction where the two walls join. It does NOT touch the roof top, but part of it does go down but the floorcarpet is not damp. It does get bigger when it rains and has warped when I saw yesterday .Could this be coming through the wall or the roof? If so, who do I call in to get this looked at? Any ideas?

If it gets bigger during rains, you have a leak somewhere above the wall. Is the wall at a valley or along the gutter? Could be water backing up over the eave and going down the wall. This is usually found in houses with no overhang and the fascia is flush with the wall.

Do you hve any plumbing pipes in this wall or above it?