What are these flies? bathroom with no windows

[Oliphantintheroom]

opened my bathroom door today and was confronted by tens of these!
Can’t investigare further without letting them all out (took picture by sliding phone through gap in door)
It’s an en suite, I don’t use the sink at all in there, or the toilet (temperamental flush) so only go in for a shower, there was a funny smell in there a few days ago, like a sewage kind of smell I think but it was a warm day and the drains outside smelled (I’m ground floor flat if that’s any relevance) so just assumed it was that and paid no more mind to it.
What are they and why are they invading my home 😫

Picture would be helpful

I would assume they are coming from your pipes if no windows. Can you use a cleaning solution down them?

How do you keep the room free of damp if there are no windows?

Can't see but are they drain flies? Like tiny moths? They breed in the sludge in drains.

They are cluster flies. They hibernate in the walls/ loft and come out when it’s warm and die.
We had them last year and it was fucking horrific

There’s an extractor fan in there for the damp.
I poured drain cleaner solution down the shower plug hole the week before last, I always do it every few weeks to keep them fresh (long hair, malt more than a dog!)

The pic isnt great but I can’t get any closer without letting them all out and don’t want them flying around my bedroom, at least they’re contained for now.
They’re quite big though, definitely bigger than regular flies, they don’t look like moths just like giant black flies that might escape and eat me in my sleep

tamtrums how did you get rid of them? Do cluster flies only come out in one room?

Man I am learning more than I would like to know about flies in the past year, we had an episode with a banana and fruit flies a few months ago!!

To deal with those, open the door a crack and spray plenty of fly spray in and close the door. Leave it overnight. You have to clear the corpses the next day and might need to repeat.

It's probs due to the heat currently! Just get some fly spray and hopefully will be the last of them!

Another pic, they are now starting to invade my main bathroom, about 8 have appeared overnight.
Again no windows and door is always shut.
This was one of the smaller ones the others are a bit bigger.
Sorry for pic overload just trying to determine if they definitely are cluster flies so I can try and deal with it myself.
Thanks for all your help so far

Do you mean they are in a separate bathroom as well? If so they are definitely in the pipes. Google “drain flies”.

They are cluster flies, and there is probably a lot more to come, sorry

We used a fly bomb from amazon because they were fucking everywhere and they are huge, they were gone after a week or so