I'd suggest the Swanley New Barn Railway, in Swanley Park, Kent.
App. 15 minutes from Swanley Station.
Open at the weekends until November.
Website is at :-
www.snbr.20m.com
Also, the Canvey Railway & Model Engineering Society will be running
their railway on Sundays until the beginning of October.
Situated in the grounds of the Waterside Farm sports centre, Canvey
Island, Essex, app. 15 minutes from Benfleet Station. (c2c).
DC