It used to be the feeder league for London & South East Premier into which the champion team each season was promoted whilst the second-placed team entered a play-off against the runner-up of London 1 North.

The champion would be promoted to either Regional 1 South Central or Regional 1 South East depending on geographical location, whilst relegated sides would go to either Counties 1 Kent or Counties 1 Surrey/Sussex.

The winner of the league after the revamp was Horsham, whilst current champions are Old Alleynians who were promoted to Regional 1 South Central for the 2024-25 season.

Joining were Dartfordians, runners-up in Counties 1 Kent (Canterbury 2XV won the league but owing to league regulations were not permitted to be promoted to Level 6), Old Tiffinians runners up in Counties 1 Surrey/Sussex and Thurrock who were level transferred from Regional 2 Anglia.

Departing were Horsham Rugby Club as champions, promoted to Regional 1 South Central.

Also leaving the league were Farnham, Guildford and Chichester - all level transferred to Regional 2 South Central.

On 30 October 2020 the RFU announced that due to the coronavirus pandemic a decision had been taken to cancel Adult Competitive Leagues (National League 1 and below) for the 2020–21 season meaning London 1 South was not contested.

[5] Departing were Sevenoaks and Brighton, promoted to L&SE Premier whilst Chobham and Tottonians were relegated to London 2 South West and Hove to London 2 South East.

Sutton & Epsom, the current champions were promoted to National 3 London & South East for the 2016–17 season, while the second-placed team, Guildford beat Tring, the runner-up from London 1 North, in a play-off for the second promotion place.

[7] Medway were replaced by Gravesend who were relegated from National 3 London & SE.

Promoted into the league were winners of London 2 South East, Tunbridge Wells[8] as well as Cobham as champions of London 2 South West and play-off winners Sevenoaks.