Labour leaders put pressure on Sadiq Khan on Friday to reconsider his Ulez extension, which was blamed for the Conservatives’ success in the Uxbridge and South Ruislip by-election.
In a surprise by-election victory, the Conservatives narrowly retained Boris Johnson’s former seat in west London.
Steve Tuckwell narrowly defeated Labour’s Danny Beales by 495 votes.
However, the Conservatives were defeated at Somerton and Frome in Somerset, where the Liberal Democrats overturned a huge majority.
Labour also won in Selby and Ainsty in North Yorkshire, with Keir Mather defeating the Conservatives by over 4,100 votes.
Mr Tuckwell said his victory was down to London Mayor Mr Khan’s “damaging and costly” Ultra Low Emission Zone expansion to the Greater London boundary.
“The message from Uxbridge and South Ruislip is clear – Sadiq Khan has lost Labour this election, and it was his damaging and costly Ulez policy that did it,” he said.
Labour Deputy Labour leader Angela Rayner also blamed Ulez for the failure to snatch the seat.
But Mr Khan was showing no signs on Friday morning of changing tack on Ulez.
A source close to the mayor said: “Winning Uxbridge and South Ruislip was always going to be a struggle for Labour.
“Labour hasn’t won this seat for five decades and Tony Blair didn’t even win it during the 1997 landslide.
“Sadiq has always been clear that expanding the ULEZ was a really difficult decision, but necessary to save the lives of young and vulnerable Londoners.”
Tory peer and pollster Lord Hayward stressed that the Uxbridge result had political implications beyond London.
He said that the swings in Selby and Somerton were “absolutely massive” but it was a “good/relieved result for the Tory Party in Uxbridge”.
He added: “One thing about Uxbridge which is interesting, is one thinks about it as Ulez and a London issue.
“But the Tories did less badly in local elections in May in places like Dartford and Thurrock.
“Ulez has implications for a string of marginals on the eastern side of London, Stevenage, Thurrock, Harlow, Dartford, Gravesend, so the Labour Party will be looking very carefully at the implications not only in Greater London but outside.”