While getting The Cornerstone online, I've gone back to find websites that link places mentioned in the book, and thus are of note in Universalist history. "Universalist London" (Georgian Nonconformist London, really) is -- as far as I can tell -- concentrated in Moorfields and a small slice of Whitechapel. Hubby indulged me over our honeymoon to visit some of these sites, which more people would know as historically Jewish London, or given the successive waves of immigrants, an area that reminds me a bit of the London version of the Lower East Side of New York City. Indeed, I wonder of the de Benneville family was there. It was Huguenot territory at one point.
You can see these, too. Look over the shoulders the sixth graders of the North West London Jewish Day School as they learn about their history at 2003 Sukkot walk. Pay attention to Sandys Row, and the synagogue there, which was once a Universalist church, and (I suspect) is where John and Eliza Murray first heard James Relly.
I also suspect the tenteryards (or a place near it) is the place where the pre-Universalist Murray attended a "Baptist society" where he met his future brother-in-law, William Neale.