Damp patch where chimney breast used to be

[nasara]

We would like to re-plaster and redecorate our upstairs hall, but there is quite a large damp patch on the ceiling where a chimney breast used to be (or so it seems - we moved in last October). Above is the loft and the remaining chimney breast. The chimney itself appears to have a cap. After a bit of googling, I'm wondering if there is something down the chimney which is retaining moisture and causing the damp. Which type of tradesperson is it best to call? I've also noticed that our neighbours who we are attached to (semi-detached Victorian house) do not have a capped chimney - could this be a cause of our damp?

We would really appreciate any help/advice as we are finding it difficult moving forward in this problem (really want this sorted before baby arrives in September and incoming bad weather of Autumn/Winter!)

 

[ree]

The term capped chimney can mean many things - typically, its an insert into a chimney stack. In your case, it would be to allow through ventilation of the redundant flue(s), and prevent bird's nesting.
However, the part of the flue in the loft should have a vent at the bottom - it should also have been swept before previous work. Sweeping removes soot which can attract dampness.

Round your stack is lead flashing (or there should be) and the chimney pot should be bedded in sand and cement flaunching. All these items need inspecting.
Whoever inspects (a roofer) should provide you with pics of the conditions at the stack and on the roof.

For now, perhaps you will post pics of the interior and exterior areas in question?