The Green Group has criticised Labour after one of its councillors crossed the floor to the Tories this morning (February 20).
Cllr Anne Meadows, who represents the Moulsecoomb and Bevendean ward, has left Labour to join the Conservative Party.
The move means Conservatives could now attempt to take control of the local authority, with 21 councillors to Labour's 20.
Read more on why Cllr Meadows made the move here: Conservatives could take over Brighton & Hove City Council as Labour councillor defects
Cllr Phélim Mac Cafferty, convener of the Green Group – which has 11 council seats – said: "Just a few months since Anne Meadows stated live on TV that she would 'not vote Labour in the next election' it is little surprise that she has defected from Labour to the Conservatives.
"Labour has been consumed by divisions: the former Labour leader Warren Morgan was ousted in a political coup, Caroline Penn quit in protest, we have had three children committee chairs in as many years and now Anne Meadows has defected. What a mess!
"In 2015 Labour promised they would get the basics right. But from overflowing bins and rampant graffiti to defecting councillors, far from ‘getting the basics right’ Labour’s many council pledges now lie in tatters.
"While splits consume the other two parties, Greens are united in our commitment to work hard for our communities and remain focused firmly on the important local issues affecting our city. It is Greens who have pushed for action on homelessness, fought cruel welfare reform, for answers on the impact of a catastrophic Brexit and forced our council to wake up to the climate change emergency.
"With Tory austerity continuing to hammer our city, and a Labour group unable to lead the council, it is the Greens who are united with a plan for the future of Brighton and Hove. Residents deserve better than Labour incompetence or a de-facto Tory council, and we look forward to sharing our manifesto for action, ready for the upcoming council election on May 2."
All 54 council seats are up for grabs in the forthcoming council election.
As it stands there are 21 Conservative councillors, 20 Labour, 11 Green, one Independent and one vacancy.
A Brighton & Hove City Council spokesperson said: "Councillor Anne Meadows has announced today that she is leaving the Labour Group and joining the Conservative Group. This changes the balance of seats held on the council.
"The current political leadership arrangements continue for now. Under our constitution, any change in leadership can only take effect following a decision at a meeting of the Full Council when all currently elected councillors agree who forms the administration and who is voted to be leader of the council. Councillors decide whether and at which meeting the business is discussed.
"Subject to the will of councillors, the day to day operation of services to the public will remain unchanged in the short term. Council officers will continue to use their delegated powers to ensure a consistent service."
More stories: Conservatives confirm Brighton & Hove City Council takeover bid
Prime Minister welcomes Brighton Labour councillor to Conservatives after defection
Labour 'extremely disappointed' after Brighton councillor defects to Tories