The original (and still current) church covenant found in the first membership book of 1925 reads:
In the love of truth and in the spirit of Jesus the Members of this Church unite for the Worship of God and the Service of Man.
In 2003 this was altered slightly changing "Man" to "humankind".
Here is a picture of the first page of the membership book. You will notice that the first signature is that of Professor F. J. M. Stratton, F.R.S. the well-known astronomer. He was the church's first chairman. His obituary is available [here].