Sir Keir Starmer has praised Sadiq Khan’s commitment to clean air in London after last year urging the mayor to “reflect” on the expansion of the ultra-low emission zone (Ulez).

The Labour leader, who lives in north-west London, said he did not want his children to “breathe in dirty air” as he appeared alongside Mr Khan for the launch of the mayor’s re-election campaign.

The Ulez scheme was expanded last August to cover the entirety of Greater London, a controversial move overseen by Mr Khan.

Health and environmental campaigners supported the bid to improve air quality, but opponents have cited the financial impact as a key concern, with the Tories also using it as an attack line against Labour.

People who drive in the zone in a vehicle that does not meet minimum emissions standards are required to pay a £12.50 daily fee or risk a £180 fine, reduced to £90 if paid within 14 days.

Sir Keir had asked Mr Khan to reflect on the policy’s impact following last July’s Uxbridge and South Ruislip by-election result, in which Labour said Ulez was a dividing issue that saw the Conservatives retain the seat.

Appearing alongside the London mayor at the launch of his campaign to win a third term in office, the Labour leader said: “I say to people who challenge me on cleaner air: I’ve got two kids. They’re 15 and 13.

“I wouldn’t give them dirty water to drink and I wouldn’t want them to breathe in dirty air.”

In a display of strengthened ties between the party leadership and the London mayor, Sir Keir said he would be able to enact “great change” with “my friend Sadiq” if Labour were able to govern from both Downing Street and City Hall.

Mr Khan has put housebuilding at the centre of his re-election pitch, opening his campaign with a pledge to build 40,000 new council homes by the end of the decade.

He touted the “rare, precious” prospect of Labour rule both nationally and in London, saying Sir Keir’s victory at the general election would mean the capital could “go from rowing against the tide of a Tory Government to having the winds of a Labour government at our backs”.

In a speech at the launch in central London on Monday, he said: “There’s been one constant – on abject failure on (the Conservative Government’s) behalf to appreciate the gravity of this crisis.

“We saw it when the last home secretary claimed homelessness is, quote, a lifestyle choice. We saw it last week when the latest housing minister said housing is never really the problem.

“After years of a Tory Government trying to drag London backwards, a Labour government would be transformative, propelling us forwards and helping to accelerate delivery of the homes Londoners desperately need and deserve.”