Burl wrote above: "The Communist Party established 'Clarion' choirs throughout the country"

I don't think this was strictly true. Clarion clubs existed in the late C19th, and pre-dated both the formation of the Labour and Communist Parties. Politically, I think they were originally aligned with the Social Democratic Federation (SDF). Like their European socialist counterparts, the SDF set up cultural activities amongst the membership, as a way of fostering community friendship and putting across socialist ideas in daily life. Bicycle clubs were one aspect (I think there are still some clubs with "Clarion" in their name), and singing groups were another. Clarion choirs, in the C20th, weren't necessarily led by the Communist Party, though CPGB members may well have taken part.

Singing groups were common amongst the left between the wars, and maybe for some time after WW2. I've an old Left Book Club socialist song book, and also one published by the Labour Party from the late 1950s. The Left Book Club volume suggests the involvement of Alan Bush (I'll check it out later and maybe report back on the songs listed, if anyone's interested). The LP book is a combination of "Early One Mornings","Old Folks At Homes", "Coming Round The Mountains"-type songs, with a few "solidarity forevers" here and there. As mild and compromising as you might expect from the Labour Party (or Old Labour as it then still was).

Down here in South East London we have The Strawberry Thieves socialist choir, who do a combination of old leftist songs, and newer self-written songs of struggle.
strawberry thieves info