I have tried to find a definitive answer for you, but without success. My great grandparents were married at St Peters in 1857. One of my grandfathers brothers is buried there (1940). I know it burnt down subsequently to 1857, but was rebuilt and is the church now. I don't know of any other building as you mention now being a private residence. Hopefully someone else will know.

The following is the link to the old chapel in Newnham which caused me to pose the question.http://churchdb.gukutils.org.uk/GLS897.php

On further investigation it does look as if it was for Non Conformists.
Thank you so much for taking the time time to reply. Ros.