Help identifying small black flies

For approximately two months now we have had an issue with small black flies congregating around the windows of the living room/dining room/kitchen (this area is open plan). Having researched online we think they are drain flies but we aren’t too sure (please see attached photo).
We have tried everything we can think of to identify the source and get rid of them with no luck (disposed of all house plants/covered the drains with tape/poured boiling water down the drains/checked the washing machine for leaks/used smoke bombs/checked under kitchen cupboards)
Please could someone confirm if they believe we have correctly identified the fly and how to get rid of them?

 

Where are you located? Location can be very helpful in insect ID, especially with the more unusual pests.

The first pic isn't helpful as it shows no detail. The second pic is good, but I've never seen wing shapes like that on a fly. Do they all look like that? Any chance we could get a pic of the underside of a dead one?

It sounds like you've done a lot of good things in order to find location, source, etc. What we call drain flies or sewer flies are technically psychoda and these flies aren't that.

Do they come out at night or daytime or no difference?

Did you tape around base of toilets as a shrinking seal under toilet can allow access sometimes?

Taking multiple specimens to the local country agricultural extension office may be the way to go here. They will be familiar with local insects as well as the common widespread insects. They are a good source of objective information.

Keep us posted.

 

Hi Pabugman, thanks for replying!
I am based in the UK and the flies are around both day and night (there are usually lots of dead ones around window sills on a morning when we wake). They seem to like the windows and don’t seem like great fliers (they almost hop around).
There are no toilets in the areas where the flies are spotted but I have taped the kitchen sink and cleaned the pipes out but no change.
I have attached a clearer photo of the bug below - I hope this helps. For sizings they are approximately 1-2mm in length
If the flies aren’t sewer flies please could you advise what you think they may be and how to get rid of them?

 

Very helpful picture showing the wing shape which is important in fly ID. This is a sewer fly. Search "psychoda". Some species have rounded wings at the tip which is common here in the states, but some species have a more pointed tip such as yours.

They live and breed in decaying, organic matter. Slow moving drains, slow rain/water leaks that aren't obvious, etc. By any chance, is there a basement/crawl space under your apt? If so, I'd want to see the sewage pipe that leaves the building and inspect it for cracks. The sewage pipe may also be in one of your walls as it goes to the basement.

Do other tenants, either above or below or beside you have this issue? That knowledge could be helpful.