The councils were first elected in 1964 and acted as shadow authorities until 1 April 1965. Each borough is divided into electoral wards, subject to periodic review, for the purpose of electing councillors. Council elections take place every four years, with the most recent elections in 2018 and the next elections due in 2022. The political make-up of London borough councils is dominated by the Conservative, Labour and Liberal Democrat parties. Twenty-eight councils follow the leader and cabinet model of executive governance, while four have directly elected mayors (Hackney, Lewisham, Newham, and Tower Hamlets). The City of London is instead governed by the City of London Corporation (and the Inner and Middle Temples, which are not governed by the City of London Corporation).