Sadiq Khan has said plans for such a charging scheme are “not on the table”, but City Hall Conservatives say they are concerned the mayor is not being honest about his “true intentions”.
Mr Khan said in September that as long as he is mayor, there will be no pay-per-mile system.
Transport for London (TfL) documents sourced by Tory assembly member Peter Fortune however refer to a scheme called ‘Project Detroit’, with its stated aims including the enabling of “forms of charging based on distance… if a decision was made in future to do so”.
Quizzed on the topic at Mayor’s Question Time, Mr Khan told Mr Fortune: “I’ve been crystal clear. A pay-per-mile scheme is not on the table and not on my agenda.
“What I said last year, and again in September, is that TfL keeps its schemes under review, that some time in the future, smarter technology might be available to simplify the current schemes like [the] congestion charge and Ulez [ultra low emission zone].
“In London, I won’t move the goalposts on Ulez emissions standards, and Londoners can be confident when they buy Ulez-compliant vehicles, that will remain the case.”
Mr Fortune pointed out that the mayor had previously said - in answer to a written question in July 2021 - that he had “no plans to extend the Ulez to outer London”, before announcing such plans eight months later, in March 2022.
The Conservative member, who represents Bexley and Bromley at City Hall, asked Mr Khan if he could give further detail on Project Detroit.
“I’m afraid I can’t, I don’t know what Project Detroit is,” the mayor replied.
Mr Fortune referred to a Freedom of Information response sent by TfL in December 2022, which explained that one of the project’s “significant milestones” is to “develop a prototype for a distance based journey estimation”.
The project is also said in the FOI response to have had a total of 97 staff members working on it as of November 2022.
Mr Fortune asked Mr Khan if he could “confirm that [Project Detroit] has been cancelled, if pay-per-mile road user charging is off the table” and whether it might be possible for assembly members to visit and speak with any technicians who may currently be working on Project Detroit.
The mayor repeated that he had not heard of the project, but said he would be “more than happy for TfL to look into the questions you’ve asked and to follow up”.
TfL’s FOI response says of Project Detroit: “We are building a new core technology platform for road user charging to replace the currently outsourced system for which the contract expires in 2026. The project is named Detroit.”
It says that the proposed platform will “replicate the capability” of existing road charges like the Congestion Charge, Low Emission Zone (Lez), Ulez, and tolls at the Blackwall and Silvertown Tunnels.
It adds: “The Detroit platform has the capability to be extended and we will be looking to build the system flexibly so that other forms of charging based on distance, vehicle type, etc., could be catered for if a decision was made in future to do so.”
Emma Best, deputy leader of the City Hall Conservatives, later told the Standard: “We don’t think pay-per-mile is the right thing to do in London.
“If that is what the mayor is pursuing, then he owes people at least the knowledge that that’s what he’s planning, so people can prepare and voice their concerns or support.”
She added: “I think that he has the [next mayoral] election in mind and he’s seeing the backlash to Ulez and that’s why he’s taken it off the table.
“That’s why I think it would be the right and honourable thing to make clear his true intentions to people so that they can vote on that basis.”
During the meeting, Mr Khan said the Ulez expansion was already working, because vehicle compliance rates have risen across the city to 95.3 per cent - up from 91.6 per cent in June.
He added: “Since its formation over two decades ago, TfL has always looked into technological and policy options regarding road pricing.
“It’s completely normal for officers to plan for different scenarios, including future mayoralties and the potential for new Government policies.
"It’s no secret that the Government and transport officials around the country, including London, have been looking at the pay-per-mile concept for some time.
“When Boris Johnson was mayor of London, his transport strategy mentioned a pay-per-mile scheme. When Rishi Sunak was chancellor, he asked his Treasury officials to look into a national road pricing scheme.”
Approached for comment on Mr Fortune's questions, a TfL spokesperson said: “Any work carried out or staff hired as part of Project Detroit has been in relation to TfL’s existing road user charging schemes. This was part of TfL’s wider work to bring in-house the currently outsourced system for which the contract expires in 2026.
"Pay-per-mile charging has been ruled out by the Mayor and no such scheme is on the table or being developed.”