2017–18 Isthmian League

The 2017–18 season was the 103rd season of the Isthmian League, which is an English football competition featuring semi-professional and amateur clubs from London, East and South East England. It was also the twelfth season for the current incarnations of the Premier, North and South Divisions, the last to have two regional divisions, and the first as the Bostik League following a sponsorship deal with Bostik.

In May 2017, the FA chose the Southern League to create one additional division at Step 3 and the Isthmian League to create one at Step 4 as part of the next change to the structure, and in March 2018, the Northern Premier League voted to reorganise its Step 4 divisions into an east-west alignment, with all Step 3 divisions contracting to 22 clubs and those at Step 4 to 20, taking effect in the 2018–19 season.

Premier Division
The Premier Division consisted of 24 clubs: 19 clubs from the previous season, and five new clubs:


 * Brightlingsea Regent, promoted as champions of Division One North
 * Dorking Wanderers, promoted as play-off winners in Division One South
 * Margate, relegated from the National League South
 * Thurrock, promoted as play-off winners in Division One North
 * Tooting & Mitcham United, promoted as champions of Division One South

Billericay Town won the division and returned to National League South after five seasons in the Isthmian League. 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.

At the end of the season a new step 3 division was created under the Southern Football League; seven Premier Division clubs were transferred to the Southern League Premier divisions. The number of clubs in the Premier Division was reduced to 22 for the next season.

North Division
North Division consisted of 24 clubs: 17 clubs from the previous season, and seven new clubs:
 * AFC Sudbury, relegated from the Premier Division
 * Barking, promoted from the Essex Senior League
 * Canvey Island, relegated from the Premier Division
 * Grays Athletic, relegated from the Premier Division
 * Hertford Town, promoted from the Spartan South Midlands League
 * Mildenhall Town, promoted from the Eastern Counties League
 * Potters Bar Town, transferred from Southern League Division One Central

At the end of the season a new step 3 division was created, thus for this season three clubs were to be promoted from each step 4 divisions - champions, runners-up and play-off winners plus one third-placed club with highest points-per-game. Hornchurch won the division and returned to the Premier Division after three seasons in the North Division along with runners-up Potters Bar Town and play-off winners Haringey Borough who never competed at such level. Due to league system restructurisation only one club was relegated from each step 4 division. Norwich United finished bottom of the table and returned to the Eastern Counties League after two seasons in the Isthmian League.

At the end of the season a seventh step 4 division was created under the Isthmian League, as the South Division clubs were distributed between new South East and South Central divisions. Four North Division clubs were transferred to South Central Division. The number of clubs in the step 4 divisions was reduced to 20 for the next season.

South Division
South Division consisted of 24 clubs: 19 clubs from the previous season, and seven new clubs:
 * Ashford United, promoted from the Southern Counties East League
 * Phoenix Sports, transferred from Division One North
 * Shoreham, promoted from the Southern Combination League
 * Thamesmead Town, transferred from Division One North
 * VCD Athletic, transferred from Division One North

At the end of the season a new step 3 division was created, thus for this season three clubs were to be promoted from each step 4 divisions - champions, runners-up and play-off winners plus one third-placed club with highest points-per-game. Carshalton Athletic won the division and returned to the Premier Division after four seasons in the South Division along with runners-up Lewes, who spent in the South Division two seasons after the relegation from Premier Division. Play-off winners Walton Casuals were promoted to the Southern League Premier Division South - the highest level they competed in their history. Corinthian-Casuals lost in play-off final but were promoted to the Premier Division as step 4 play-off final loser with highest points-per-game ratio after Thurrock from Premier Division folded. Corinthian-Casuals last competed in top division of the Isthmian League in the 1973–74 season. Due to league system restructurisation only one club was relegated from each step 4 division. Shoreham finished bottom of the table and returned straight back to the Southern Combination League.

At the end of the season a seventh step 4 division was created under the Isthmian League, as the South Division clubs were distributed between new South East and South Central divisions. The number of clubs in the step 4 divisions was reduced to 20 for the next season.

League Cup
The 2017–18 Alan Turvey Trophy (formerly the Isthmian League Cup) was the 44th season of the Alan Turvey Trophy, the cup competition of the whole Isthmian League.

Calendar
The Isthmian League Cup was voluntary this season, nine clubs decided not to take part in the competition:


 * Cray Wanderers
 * Dereham Town
 * Guernsey
 * Hastings United
 * Lewes


 * Lowestoft Town
 * Needham Market
 * Norwich United
 * Thurrock

First round
Sixty two clubs participated in the first round, while one club received a bye to the second round:
 * Hendon

Second round
Thirty clubs to have made it through the first round were entered into the draw with two clubs who get a bye, making thirty-two teams.