The Labour leader on Saturday called for “reflection” on how the expansion of the charge on polluting vehicles would be carried out after the party was beaten by the Conservatives in Boris Johnson’s old seat.
Labour overturned a huge 20,000 Conservative majority in the North Yorkshire seat of Selby and Ainsty but fell short in Uxbridge by 495 votes.
The loss prompted senior Labour figures to question Mr Khan’s proposals to extend Ulez to all London boroughs. It currently only applies to central London and the areas up to, but not including, the North and South Circular Roads.
The rollout will widen the £12.50 daily charge for cars which fail to meet emissions standards to beyond the capital’s north and south circular roads.
Speaking on a visit to Shefford in Bedfordshire, Sir Keir told broadcasters that there was “no doubt” that the party lost the by-election because of the Ulez expansion.
“I have said we should reflect on this, including the mayor. I have spoken to him as you would expect, and so there will be that reflection.”
Asked whether Labour’s green policies would be under review, the Opposition leader said there would be no scaling back but that consideration was required as to how policies were enacted.
“I think when it comes to green commitments, it is not a question of whether they should be done – of course they need to be done.
“It is how they are done, so there is a discussion to be had about that.”
Sir Keir told Labour’s national policy forum in Nottingham that there was “something very wrong” when a party policy was on “each and every Tory leaflet”.
“We’ve got to face up to that and learn the lessons,” he added.
His criticism of the policy was echoed by Labour’s deputy leader Angela Rayner, who said the party had lost because it failed to “listen to voters” over Ulez concerns.
Labour’s Uxbridge candidate Danny Beales said the Ulez expansion had “cut us off at the knees”.
A source close to the Labour mayor said: “It is a disappointing result and Sadiq has been clear he is listening to Londoners following this by-election.”
On Friday, Mr Khan said he was “disappointed” that the party did not win the seat but insisted that the decision to widen the Ulez was “the right one”.
“It was a difficult decision to take. But just like nobody will accept drinking dirty water, why accept dirty air?”
Ulez was first proposed by Mr Johnson in 2015, during his stint as London mayor. He said it was “an essential measure to help improve air quality in our city, protect the health of Londoners, and lengthen our lead as the greatest city on earth”.
Prime Minister Rishi Sunak and Sir Keir were on Saturday urged not to water down environmental commitments despite the Tory’s success in the by-election.
Tory MPs have called for Mr Sunak to re-examine the Government’s pledge for the UK to have a net zero carbon economy by 2050.
An ally of the Prime Minister told The Times that Mr Sunak would approach the lead-up to next year’s likely election with “more political edge” in recognition that “substantive issues”, such as Ulez in Uxbridge, could help the Tories to win.
But Chris Skidmore, the UK Government’s net zero tsar, warned ministers against “playing politics” with environmental issues, arguing it could cost the Tories in the long run.
The Conservative MP told PA: “To do so would not only be deeply regrettable, it would be an abdication of responsible government that must put the lives and health of the public, and the opportunity for economic growth by investing in industries of the future, ahead of gamesmanship.
“It is also really bad politics, given that the environment and taking action on climate change consistently polls third in the issues that voters care about.
“Mainstream parties that don’t recognise the priorities of the public and are instead swayed by vocal minorities end up ultimately becoming minority parties in due course.”