Dave
Just had a look at the holdings in the ESRO - looks like the records that you require have not been deposited as they seem to start in 1907 for Mayfield
United Reformed Churches (Congregational): Alfriston from 1801; Boreham Street 1897-1946; Brighton and Hove, Clifton Road 1864-1927, Cliftonville from 1863, London Road 1846-1943, Queen Square 1856-98, Union Church 1898-1964, Union Street 1699-1898; Burwash 1766-1968; Eastbourne, Pevensey Road 1861-1973, Upperton Road from 1885; Hastings and St Leonards and East Sussex Auxiliaries (London Missionary Society) 1888-1908; Heathfield Independent 1814-1946; Herstmonceux 1811-1975; Lewes, the Tabernacle from 1816; Mayfield 1907-1983; Sussex Congregational Unions and Missionary Society: Eastern District 1890-1972; Sussex Home Mission Society 1922 (NC)
Chris in 1066