National Council of British Socialist School Unions.

Socialist Sunday School Song Book

Socialist Sunday Schools were a popular form of social activity from the early 1900s to the 1950s. They taught socialism instead of religion. Their ideology appears to have been Fabian(or at very least not class struggle marxism or anarchism but something safe and unoffensive)

Reproducing here for historical interest and value. This should not be taken as my agreement with their politics.