A South Downs walk, first visiting Arlington Reservoir (good for ducks) then Wilmington, famous for its hillside figure and churchyard yew. The church has a charming "bee and butterfly" window. After tickling the Long Man's toes, you're off across the downs, through Jevington, a historic smuggling village, and eventually down to the sea at Eastbourne.
It is possible to do a shorter (11.6 km 7.2 ml) walk, finishing in Polegate.
Hardnuts could extend the walk to include Beachy Head, but you lot don't strike me as hardnuts.
Trains: 9:55 from Victoria (Clapham Jct 10:02, E Croydon 10:12) to Brighton, change there to the Eastbourne train (arr 11:01 plat 4, dep 11:05 plat 7) arr Berwick 11:32. You don't get long at Brighton so don't mess about.
For a more leisurely interchange, you could get the 9:46 Ore train from Victoria (Clapham Jct 09:53, E Croydon 10:03) and change at Lewes onto the same Eastbourne train (arr 10:49 plat 1, dep 11:21 plat 3).
Return from Eastbourne at xx00. Get a return to Eastbourne.
Tea: In Jevington, choose between the Eight Bells and the Jevington Tea Room.
It shouldn't be hard to find somewhere in Eastbourne. The Qualisea Fish Restaurant on Terminus Road comes recommended.