Theres a couple of good contenders on the GA network:
Real-time train running information for 5J10 0738 departure from London Liverpool Street to Wickford on 14/10/2026. From Realtime Trains, an independent source of train running info for Great Britain.
www.realtimetrains.co.uk
This one goes ECS at 07:38 Liverpool Street to Wickford to form the 08:16 to Southminster. Running it in service fron Liverpool Street would provide direct connnectivity from London to the likes of burnham on crouch and would remove the need to lock the train out of service at Liverpool Street
The 06:48 and 07:35 Wickford to Southminster services come ECS from Ilford depot so could probably run in service from Shenfield. These are DOO so no extra crew needed.
Real-time train running information for 5F65 1936 departure from Walton-on-the-Naze to Colchester on 14/10/2026. From Realtime Trains, an independent source of train running info for Great Britain.
www.realtimetrains.co.uk
This one from Walton-on-the-Naze to Colchester even runs via Colchester Town and would connect into a clacton service st Thorpe-le-soken
Real-time train running information for 5N03 0758 departure from Clacton-on-Sea to Walton-on-the-Naze on 18/10/2026. From Realtime Trains, an independent source of train running info for Great Britain.
www.realtimetrains.co.uk
This one on a sunday morning would give an earlier service to the Walton-on-Naze branch from Clacton
Meanwhile up on the Wherry Lines 5D26 at 22:40 from Lowestoft to Norwich Crown Point which runs via Norwich station would, if run in service, neatly fill in a 2 hour gap in Lowestoft to Norwich services on a Sunday evening (21:47 - 23:35).
Real-time train running information for 5D96 2240 departure from Lowestoft to Norwich C.Pt. T.&R.S.M.D on 18/10/2026. From Realtime Trains, an independent source of train running info for Great Britain.
www.realtimetrains.co.uk
Not sure if that one has a guard onboard or not. Does Lowestoft have a traincrew depot?