[1] The Premier Division consisted of 20 clubs, the same as last season, and featured three new clubs after Bristol Manor Farm were promoted to Southern League Division One South & West, Gillingham Town resigned from the league, and Sherborne Town were relegated to the Division One.
Of the fourteen runners-up, the twelve clubs with the best PPG (points per game ratio) were also to be compulsorily promoted, but with resignations and mergers in leagues above, all runners-up were promoted.
All Step 5 leagues were fixed at 20 clubs for 2018–19, but in this case there were no further relegations or reprieves.
The First Division consisted of 22 clubs, the same as the previous season, and featured two new clubs after the promotion of Hengrove Athletic and Wellington to the Premier Division: Step 6 clubs without ground grading Grade G were to be relegated to Step 7, but no club in this division failed the ground grading process.
All Step 6 leagues were fixed at a maximum of 20 clubs for 2018–19, but in this case there were no further relegations or reprieves.