Damp -upstairs room of 1870 house.

stuart45

You can get insulated plasterboard.

FFHillbilly

I deal with this all the time. most of the time that can be solved by turning up the heating and opening the windows more often. I've definitely seen more of it since the price of energy went up in 2021 which is understandable.
I've been to 2 (approx 100 year old) houses for 2 different landlord in the past month, both of the tenants are struggling with mould and mildew which looks pretty similar to the OP's pics, and coincidently the landlords are both ex residents of those houses and say it was fine when they were there and presumably used the heating more and opened windows more often. 
both houses also stunk of air fresheners and scented candles, I can't back this up with any science but I wouldn't be surprised if there was something in them that might make mould or mildew more likely, they definitely reduce the air quality. if anyone does use these check out the VOC rating on it and see of you want to live with them anymore....

honest advise would be to spend £500 more on your energy bill every year and see if it goes away, thats half of what you've been spending now based on your "£10k in 10 years" statement
you could spend some money on PIV units or extractor fans to improve the airflow, but you could also just open the doors and windows more often which is free(initially, although you'll need more energy to keep the house at 20 degrees when you do this in the middle of winter)
If your windows have trickle vents open them, most windows also have a slightly open but locked feature which increases airflow

fluffymuffy

We managed to overcome a similar problem by using a dehumidifier running constantly on the landing.

Nevbear

The roofer said it was condensation but I wasn’t convinced due to the distribution of the patches but it makes sense now

It’s a big house and I pay £360 a month for gas and electricity already. I don’t mind the cold - all my houses have been cold period homes but I’m fed up of shoes growing mildew

greyteam1959

PIV would probably be worth fitting I would think.
I had similar problems & it cured them.
If you could fit it yourself you would be looking around £350.

Nevbear

Daughter’s boyfriend’s dad is a surveyor apparently so I’m going to chat to him tomorrow about any local recommendations. I think he’s commercial rather than residential. 

I’m hoping it is condensation rather than water ingress rotting my houses structure. 

Newbie_John

What's the temperature in the room?
Is it all year round or just more visible in winter?

As mentioned earlier I'd buy a dehumidifier - they cost about £150 and just let it run.

Nevbear

More visible in winter 
it’s a big house and only 2 of us now. We have a heated floor in the kitchen diner and only use a small sitting room if we want to watch TV so use the gas fire in there. I guess it is worse as we are heating less in general over the last couple of years or so. 

Overall, I’d prefer to get the plastering redone rather than keep using the dehumidifier but I’ll see what a surveyor says about it

yes it’s overall about 10k including the re rendering of all of the chimney, the pots changed at another time, the areas at the bottom of chimney down towards the gutters done 3 times (!) plus the other parts from the roofer on a loose tile and gutterings. The scaffolding costs add up too 

flashg67

Even removing the paint and using lime wash paint might help - it has for me in an old house. I have a small space heater on a timer too to keep the area warmer which helps. I've had good success with insulated wallpaper - cheaper than replasterboarding and worth a go. Hanging wardrobe dehumidifier bags have helped us too

stuart45

Is the back of the wardrobe where the chimney breast was?