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. •
Bridgwater Town, relegated from the
Southern League Division One South & West. •
Hengrove Athletic, runners-up in the Division One. •
Wellington, champions of the Division One. With the suspension of ground grading Grade E for this season and the creation of a new league at Steps 3 and 4, the champions of all Step 5 leagues were compulsorily promoted to Step 4. 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. Teams at Step 5 without ground grading Grade F were to be relegated to Step 6, but no club in this division failed the ground grading process. All Step 5 leagues were fixed at 20 clubs for 2018–19, but in this case there were no further relegations or reprieves.
League table Stadia and locations ==First Division==