In 1985 Bellos was elected as a Labour councillor to Lambeth London Borough Council and was leader of the council between 1986 and 1988. She was the second Black woman to become leader of a British local authority, after Merle Amory in the northwest London Borough of Brent. Bellos resigned as leader on 21 April 1988, after disputes within the Labour Party over the setting of the council budget. She was a prominent figure in left-wing politics in London in the 1980s and was labelled by "The Sun" as a member of the "Loony Left". Bellos attempted to become a parliamentary candidate, without success, most notably for Vauxhall, south London, in the Lambeth borough, where there was a by-election in 1989, following the resignation of Stuart Holland MP. Fellow Black Sections vice-chair Martha Osamor was chosen by the local party to be the prospective parliamentary candidate but she was rejected as too left-wing by Labour leader Neil Kinnock, who got Kate Hoey imposed by the national party.