I doubt whether there was a multi-religious school Sqad. In yours the Catholics used to be separated less they heard Protestant dogma at prayers. In mine , the Jews and some Catholics did not attend the religious part of morning assembly.
The Education Act , 1944, made it compulsory for schools to have a morning assembly which was broadly Christian in character (and we knew which branch of Christianity was contemplated) and the same applied to religious education, also compulsory. These provisions have only been changed in recent years, to accommodate the fact that many families have no religion and many more are not Christian, the school being multi-faith in its intake or predominantly non-Christian.