A decision by Britain's governing party to get a lawmaker elected by attacking London's flagship anti-pollution policy has raised questions over whether the country's green agenda risks being derailed at the next national election.
The Conservative Party has embraced reaching net zero by 2050, while the main opposition Labour Party says it has more ambitious plans for 100% clean power by 2030.
But their candidates in Thursday's byelection in the constituency of former Prime Minister Boris Johnson both disavowed the expansion of London's Ultra Low Emission Zone (ULEZ), planned for next month by the capital's Labour mayor, Sadiq Khan.
National Labour leader Keir Starmer, whose party is comfortably ahead in national opinion polls, said the expansion plan had been decisive in his candidate not winning in the Uxbridge and South Ruislip constituency.
"We heard that on the doors," he said. "And we've all got to reflect on that, including the mayor."
Under Khan's scheme, the zone will become one of the world's largest to tackle pollution, encompassing 5 million extra people in the capital's leafier and less-connected outer boroughs.
The vast majority of vehicles will be exempt, but those whose emissions exceed the pollution threshold will have to pay 12.50 pounds ($16) a day.
Prime Minister Rishi Sunak - whose lukewarm embrace of the green agenda has been criticised by some in his party - last month criticised Khan for imposing ULEZ "against the overwhelming views of residents and businesses."
Tony Travers, director of LSE London at London School of Economics, said that while the anti-ULEZ strategy had worked in Uxbridge, it seemed unlikely that broader opposition to green policies would benefit parties at the next national election expected in 2024.
"I doubt there are that many votes in an all-out assault on government's green priorities... partly because so many of them are abstract enough to be far enough in the future," he told Reuters.
Both main parties have struggled to present a consistent front on the environment.
While Starmer and Khan are at loggerheads over ULEZ, the original policy was planned by a Conservative - Johnson himself while he was London mayor.
Theresa May's Conservative government then adopted a commitment to reduce greenhouse gas emissions by 100% from 1990 levels by 2050.
But international environment minister Zac Goldsmith quit recently, saying he had been "horrified" that the government had stepped away from commitments, labelling Sunak as "uninterested" in leading on environmental matters.
For his part, Khan said on Friday that the policy to expand ULEZ remained the right one.
"It was a difficult decision to take. But just like nobody would accept drinking dirty water, why accept dirty air," he told Sky News.
