There's a singaround session in the lounge of Laurieston Bar in Glasgow on Monday nights.

21-23 Bridge Street (just south of the Clyde)

Link to Google Map

Don't be dismayed by the fairly dismal locale. The bar staff are congenial, providing complimentary tea, biscuits and (last Monday) toasted cheese, and the session regulars are welcoming. Expect a wide range of genres and abilities.