Penetrating damp

[Labracadabra]

We viewed a house yesterday which meets a lot of our needs (which is rare!) but it's definitely a refurbishment project (although the blurb describes it as "extremely well presented throughout" ). However, the main problem on first inspection is that there is significant penetrating damp around the chimney area. It's clearly visible on wallpaper/plaster in one of the bedrooms and the upstairs hallway. The vendors say it's been like that for a while and they've had it investigated and flashing/flaunching etc all fine. The chimney and flashing and roof all does look to be in good condition when viewed from the ground by a non-expert (i.e. me!) but clearly the water is getting in somewhere so there must be an issue.
How should we proceed? Should we get a roofer/builder/surveyor/damp specialist to examine it at this stage? If so, which professional is best for this? We want to know roughly what we're dealing with before putting in an offer (as we'd need to account for the costs of the work). It's overpriced at the moment (of course!). Thanks!

Ask the EA for a list of builders/roofers who could give quotes.

I'd say get a surveyor or builder/roofer. Don't get a damp specialist in, well the sort that sells the chemical dpcs etc. our friends had this issue and it turned out to be something to do with the aerial which was attached to the chimney- there was an issue with the fixing and water was pouring down. Also are the fireplaces still there or if not do the chimney breasts have any vents in them? That can also be an issue.

chimneys get damp from internal condensation if they are not effectively ventilated top and bottom. Is it?

If the chimney is not on an external wall that is the most likely source (unless there is a water leak, which is rarer).

Damp chimneys usually leak hydroscopic salts, and yellow tar stains, in which case all the affected plaster has to come off and be replaced after drying out. That is messy but not expensive.

Thanks all! PigletJohn, how can we tell if it's condensation rather than a leak? Is condensation usually black mould (this isn't)? The chimney isn't on an external wall though (it's in the middle of the roof) so it sounds likely from your description.
The latest measure the vendors have taken is to have an air brick fitted into the (internal) wall of the bedroom - presumably this would only help if it's condensation, not damp? It does sound as though they've tried to sort it, as presumably having the air brick fitted was quite messy and they wouldn't have bothered unless they thought it would help.
Are there any tests/things we can look for at our second viewing to determine whether it's condensation or damp?
Thanks again everyone!

condensation is damp

if there was a leaking pipe, there would tend to be one very noticable wet area, and it would be close to, or underneath, where the leak was.

chimney condensation will tend to be a broad area of slight dampness or staining, usually yellow, with no particular centre to it, though sometimes you can see the shape of the bricks, and seems to happen more often downstairs, and near the ceilings.

but if the chimney has not been ventilated top and bottom, you can expect condensation.

Thanks very much! I'll take another look with that in mind