The Conservatives have picked local councillor Steve Tuckwell as their candidate for the Uxbridge and South Ruislip by-election, and on Friday he immediately launched a double attack on Sadiq Khan's Ulez extension.
The Tories are seeking to turn the vote on July 20 to choose a new MP, after Boris Johnson quit, as a "referendum on Sadiq Khan's Ulez".
Responding to his selection, Mr Tuckwell said: "I'm honoured to be selected to represent the area I have served since 2018 and grew up in.
"Uxbridge cannot afford a Labour MP who backs Khan's plan to stop residents living their lives the way they choose and make us pick up the tab for his mistakes, under his Ulez expansion. I'm a local here, and if elected, I will work hard to deliver the rebuilding of Hillingdon Hospital."
Cllr Tuckwell, who is chairman of Hillingdon's Major Applications Planning Committee, added: "If Labour win in Uxbridge however - it will send Sadiq Khan a clear message that he can expand his Ulez and close our police station."
Labour's candidate Danny Beales, who grew up in the area but is currently a Camden councillor, has responded to the Tory Ulez focus by stressing that it is not a "binary issue" for local people.
"People are concerned about air quality and pollution and their children developing asthma and getting ill, but people are also concerned, in this cost of living crisis, about having to pay an extra charge to drive," he said.
He added: "The Conservatives may want to run a single issue campaign here, but I don't think that will wash with voters.
"The Conservatives tanked the economy and people here have seen their mortgages rise sharply. "They are concerned about their pensions. Nurseries and children's centres have closed down. And where is the new Hillingdon Hospital that was promised?"
The Ultra Low Emission Zone, to clean up the capital's air, will be expanded to cover outer London suburbs at the end of August, with a daily £12.50 charge for non-compliant vehicles.
Mr Khan has faced criticism for bringing in the extension too swiftly, and so giving motorists insufficient time to replace their vehicle, but has expanded a scrappage scheme in response to a backlash against it.
The by-election was called after Mr Johnson resigned as the local MP ahead of a damning report by the Commons Privileges Committee which found that he deliberately misled Parliament over the "partygate" scandal.
It recommended that if he had still been an MP that he be suspended from the Commons for 90 days, partly because of having committed contempt of Parliament in his scathing response to the report after being handed a draft of it.
The Tories won the Uxbridge seat with a majority of 7,210 in 2019.
There is also a by-election in Selby and Ainsty in North Yorkshire, where the Conservative majority was 20,137, after close Johnson ally Nigel Adams quit there.
Ex-Culture Secretary Nadine Dorries, another close ally of Mr Johnson, has said she would resign as MP for Mid-Bedforshire, where the Tories have a majority of 24,664, but is yet to do so.
Register now for one of the Evening Standard's newsletters. From a daily news briefing to Homes & Property insights, plus lifestyle, going out, offers and more. For the best stories in your inbox, click here.