Essex/Canterbury Jack 1 is an English Rugby Union league at the ninth tier of the domestic competition and features teams from Essex and parts of north-east London. Promoted clubs tend to move up to London 3 Essex. Relegated clubs used to drop into Essex Spitfire 2 but as that division has been abolished there is currently no relegation. The division was created in 2003 by Essex-based teams who left Eastern Counties 1 and Eastern Counties 2.
For the 2016-17 season the league was divided into two parallel divisions - Essex 1A and Essex 1B - divided on geographical lines with teams in Essex 1A typically based in the north and east of the county, while teams in Essex 1B are predominately London based. Each division plays 14 home and away games from September until February. From February the top 4 teams from each division go into the Essex Canterbury Jack 1 Premiership and play for the title and promotion, while the bottom 4 sides from each group would play for the Essex Canterbury Jack 1 Shied.
From 2004 to 2016 there was a play-off between the runners-up of Eastern Counties 1 and Essex Canterbury Jack 1 for the third and final promotion place to London 3 North East. The team with the superior league record had home advantage in the tie. At the end of the 2015–16 season the Essex Canterbury Jack 1 teams had been the most successful with seven wins to the Eastern Counties 1 teams five; and the home team had won promotion on eight occasions compared to the away teams four. Since the introduction of London 3 Eastern Counties and London 3 Essex at the start of the 2017-18 season the playoff has been cancelled.
Eastern Counties 1 v Essex Canterbury Jack promotion play-off results