There is a tiny pub in a tiny fishing village on the northumberland coast where there is a session on the last Monday of the month. This is mainly attended by musicians, but the organiser does as his job infers, he organises the night. A few tunes from all assembled then a couple of songs then tunes and so on. A great night and you don't have to announce your presence as he asks.
Another folk club on the Northumberland coast hosts pipers guitarists singers, of many genres, and again the organiser mixes them up without any complaint.