As well as the records of the British Humanist Association, the Alternatives to Religion Project includes the records of Conway Hall Ethical Society (CHES).
Here are just few of the minute books created by the predecessors of CHES. The minutes start in 1807 and trace the evolution of the ethical movement from a congregation of Unitarians and Presbyterians to the humanist membership of the Society today.
Conway Hall reference: SPES/1