The Conservatives suffered a second loss in London when the leader of Barnet Council conceded defeat.
The north London borough was Labour's top target in the capital and is where leader Sir Keir Starmer launched his party's London campaign.
Labour's chances of taking control in 2018 were badly damaged by allegations of antisemitism under former leader Jeremy Corbyn.
Sir Keir will regard today's victory as a significant milestone in his party's efforts to rebuild trust with London's Jewish community.
The result is likely to alarm Barnet's three Conservative MPs, Theresa Villiers, Matthew Offord and Mike Freer.
Barnet Conservative leader Daniel Thomas said Labour's win "does not bode well" for the Tories at the next general election.
"I think this is a warning shot from Conservative supporters," said Cllr Thomas.
He added: "Clearly if Labour are to get a majority in Parliament, they need to win Barnet. They won the council, if they win our parliamentary constituencies as well, then it doesn't bode well for us to form a Government in future general elections."
What You Need To Know - listen to the latest episode