Damp on wall near Window

[Augustus]

I've had a look at various other threads on this topic and still can't see what the cause of my problem is. Basically, the plaster on on internal wall of an upstrairs bedroom has got damp and the paint is flaking. The area where this is happening is confined to the end of the wall where there is a upvc sash window.

I've had a look outside and there is nothing immediately apparent that would cause penetrating damp. The pointing is all good as is the stone and I can't really see any problems with the sealing around the window.

I've attached pics of the wall where I'm getting the problem and of the outside

I cut a small hole in the plaster to take a look inside & it looks like this is dry lined as it's attached directly on to a solid wall indicating that maybe there have been issues in the past. Also, I do get some condensation and a bit of blackspot mould around the window recesses in this room and others but this is much more severe and concentrated in the area near to the window.

Any suggestions would be very welcome

 

[^woody^]

I'll put 50p on condensation.

 

[Augustus]

i put a couple of coats of Ronseal anti condensation paint on that wall and 2 months later it still seems to be holding up