Thanks for the help on this one guys.
The temp does not vary much as the stove is kept in over night.
The readings I have taken are after the ply cover is taken off so no real idea what things were like in there before.
On our balcony I have still not got around to putting a cover over the foil and we have no problem here, this adjoins the bedroom where the problem is.
My hope is if I replace the ply top and seal all the edges the warm damp air will not get to the cold surfaces to condense.
The infra-red thermometer is the B&D heat detector. You can get much cheaper ones on Ebay but it was a Christmas present to myself so I got the one with
the fancy lights
In the main sitting room the wall cover is caulked in I could lift one of these off to see if the problem occurs when air finds it difficult to get to the cold surfaces.