They are the principal authorities in Greater London and have responsibilities including education, housing, planning, highways, social services, libraries, recreation, waste, environmental health and revenue collection.

[2] A Labour councillor for Glyndon, Tonia Ashikodi, was given a suspended sentence for property fraud in March 2020.

[5] The council's finance cabinet member and a Labour councillor for Shooters Hill, Chris Kirby, announced his resignation in January 2021.

[6] A Labour councillor for Greenwich West, Mehboob Khan, announced his resignation in February 2021 due to taking a politically restricted job working for Redbridge London Borough Council.

He had previously been the leader of Kirklees Council in Yorkshire, remaining a councillor there for some time after moving to Greenwich [7] and had served on Greenwich council since 2015 [8] By-elections to fill all vacancies were held in May 2021 alongside the 2021 London mayoral election and London Assembly election.

All registered electors (British, Irish, Commonwealth and European Union citizens) living in London aged 18 or over were entitled to vote in the election.

[12] The by-election was triggered after the resignation of Cllr Sammy Backon due to taking a new job outside of London.