Dulwich Hamlet, who competed in the Isthmian League since its establishment in 1907, won the play-offs and followed them.
Only one club was relegated from the Premier Division; Tooting & Mitcham finished bottom of the table and returned straight back to step 4.
Play-off winners Walton Casuals were promoted to the Southern League Premier Division South - the highest level they competed in their history.
Shoreham finished bottom of the table and returned straight back to the Southern Combination League.
The Isthmian League Cup was voluntary this season, nine clubs decided not to take part in the competition: