I knew that he was a member of The Children of God/The Family International and he did an album called Jeremy Spencer and the Children in the early 1970s. As far as I can tell, it’s probably true that he played on the 1985 album This Must Be Heaven, which is the one with Cathy Don’t Go on it. I can find lists of people who contributed to the album on various sites, and they include him, but I can’t find any credits for individual songs.

https://www.nubeat.org/abhmtmbh.html

I haven’t spent that much time on it, but it’s not easy to find a complete scan of the liner notes. I think people are just saw that he was involved in some way and then started making claims that he was the main person behind it because he’s the only one who’s independently famous.