How worried would you be about this?

It needs attention OP, but I don't think it's a catastrophic amount of damage, you've just got a leak somewhere. Our kitchen ceiling was worse than that just before we had the bathroom done, it was letting shower water through the very old wall panels, and the kitchen is directly underneath the bathroom 🤦‍♀️. It's all resolved now we've had the bathroom done, and watertight again. I'm sure once you find the source of the leak and get it sorted, it'll dry out and you can sand and paint it. You may need a special paint, as normal emulsion might not cover the stain. Sometimes the staining comes through, so you might need to use something like Ronseal one coat damp seal, or a cheaper option is to mix PVA glue in with the paint, which is what we do, as we get a few damp patches here and there - it's an old build.

I had similar and it was a loose roof tile, I called a roofer, he had a drone and looked at it that way. He did a quote then came back and fixed it.

Fair enough. I hope you manage to solve it easily.

Pls call a recommended roofer and ask them to check the roof and guttering asap. It could be a few slipped/ displaced tiles, blocked guttering or something worse. The longer you leave it, the more expensive it becomes xx

In my case, I need a damp specialist to diagnose whether it is raising damp or penetrating damp and potentially have membrane replaced. I pretty much suspect that the culprit is a terrace the previous owners built. A builder is not going to help me at this stage.
My point was, that looking at the situation and getting anxious is not going to get it fixed. A professional needs to come out and have a look. In op's case it is likely to be a roofer although, a dump surveyor will absolutely diagnose this Then, once all information is available, the OP can make a plan. None of us can diagnose this from the picture, we can simply offer our best guess. I am glad to see that someone is coming out to her on Wednesday and, hopefully, it's not a big repair.
My former landlord had a lot of work done when we had a similar issue and went through a number of builders each of whom had their own hypothesis. So he ended up doing quite a lot of work including entire facade redone with moisture resistant render and, a year later, removal of the chimney breast. It didn't fix the problem. So I would rather pay for a damp survey and know exactly what the issue is before I throw more money at the builder.

Bear in mind that where you see the damp may not be where the water is coming in. It travels to the point of least resistance. I had water damage in the sitting room but the bathroom radiator was leaking. It's probably something minor, but definitely get 3 quotes.

If the guttering is broken or stuffed full and blocked then yes they'd be able to diagnose. You could try this and then if they say gutters are all fine then it will most probably be the roof.

I apologise if this isn’t helpful as I don’t know who exactly I would call but in my experience, damp specialists, tend to find damp. Regardless.

Maybe a nice local builder?

There is no point in worrying or panicking - it's not going to help to sort the issue. You need to stop speculating what it is and call a professional to make an assessment.
I currently have a wall in my living room which has moisture reading higher than the rest of the house and some salt deposits. The worst thing I can do is look at it and panic. I have a list of damp surveyors to ring up on Monday morning so I can figure out what is going on and deal with it appropriately. Also a single female with absolutely no clue what I am looking at. That's why I need a professional.

We had similar and it was a problem with the flashing around the chimney, can't remember if it was cracked or actually missing.... Got it fixed by a roofer, the ceiling dried out and we repaintand it's been fine since.
Can you send the person the photos and ones showing the outside to see if they are the right trade to look at the problem before they come round?

You could contact your house insurance and see if it comes under buildings part

It could just be one tile a cracked tile

It could just be a bit of flashing or a cracked tile. Try not to worry until you know more, but it will need fixing.

Honestly OP if you don't sort it now then it's going to cost potentially a whole lot more after the winter. Don't bury your head in the sand any longer - it won't go away on its own.

Do you have a local facebook group? People can be super helpful and someone may just be able to pop round for you and see what the issue is. Explain the problem and share a pic and explain that you're worried and on low income etc. It is going to cost you though to get it fixed but it will cost you way more in the future if you don't get it fixed now.

Might just be a missing/slipped tile, blocked gutter or a bit of reppinting. Don't automatically assume the worst!

Get someone up there you can trust and ask for video evidence if they are quoting you to fix it. I learned how to do most of these kinds of jobs on my home, as tradies are so expensive, take the utter piss and are total fucking letches 80% of the time. Good luck!

Could just be a steamy point in your room where wet warm air hits a cold wall/ceiling. Open the windows, use a mould killer and scrub it all back, paint it with mould stuff and then paint with barrier paint then repaint the ceiling.

It's one of those 'a stitch in time saves nine'. If you get it sorted now before the winter it will be far cheaper than if you leave it to get worse and still have to get it done. 200 or 300 might sort it.

Wait until it's raining hard then get up into the loft and see what is happening. It might just be a broken or lose tile but it needs sorting before it causes a ton of damage. If you can get a dehumidifier to dry it out you could use special damp paint then paint over it once it's dry. You must sort leek out first though.

It might just be a cracked or missing tile. You definitely need to get someone to look at it before it becomes a big problem. A roofer would get up on the roof and check the tiles and gutters and probably wouldn't charge for coming to look at it. It will cost you less to get it fixed than you will lose if people drop their offer price to fix an unknown problem.

It looks like you have a leak. You need to get it looked at before it gets worse.

OP, can I suggest that you take a look at this website, all you need to do is enter the type of trade you're looking for, and your postcode, and it comes up with a list of tradespeople that is vetted by Trading Standards.

https://www.buywithconfidence.gov.uk

You have a leak in your roof, gutters or brickwork. Just get it looked at, OP – leave it and the more penetrating damp will get in and it will get more expensive to fix.

@Hhousee Call your insurance company - claim on your contents / building being damaged by a leak. They’ll send someone to assess the damage and tell you if you’re covered or not.

This happened to us many moons ago and our insurance paid for the leak to be fixed and for our bedroom to be redecorated.