Damp on Chimney in Attic

It's a ~100 year old terrace house.
Just had an entire new roof, flashing etc and both chimney's re-pointed (by a different builder than the roofer), including the lowering and rebuild of the one which is affected here. (As it was well over 10ft tall!)

Both were done a couple of months ago while the weather was dry. Now we're getting some rain I have noticed this problem.

I don't know whether it's likely the roofer and his flashings that are a problem, or the brickies who did the chimney re-point.

By the way, the bit where the plaster is off is what I've done, as getting ready for a new ceiling, however obviously I'm reluctant until this is resolved.

Any ideas what might be the cause, or is it too hard to tell?



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Looks like too much water for seepage through the brickwork. However many old stacks had no water barrier.
The obvious shoice would be the flashings.
Get some Mangers "Stop That Leak" to make a temporary fix but forget the ceiling until this is sorted.
(You might try to exose the tile line from beneath by cutting back the insulation boards)