The charge was “temporarily” hiked from £11.50 to £15 last June, and its hours were extended until 10pm, including at weekends.
Sian Berry, the Green candidate for mayor, told the Standard: "These comments show that the current mayor simply isn’t serious about cutting traffic in London.”
Luisa Porritt, the Lib-Dem mayoral candidate, said: “This is a backwards-looking mayor with no forward-thinking plan for London’s recovery. How can we take Khan’s self-professed green credentials seriously when he’s plotting a dangerous and unfair car-led recovery?”
The move is a surprise as Mr Khan’s aides had previously suggested the extra income from the C-charge would be used to subsidise free travel for under 18s and over-60s, which is no longer funded by Government.
Retaining the £15 levy and longer operating hours beyond the autumn – the charge normally operates 7am to 6.30pm Monday to Friday – would have to be approved by a Londonwide consultation.
It suggests Mr Khan is not prepared to risk asking Londoners to accept a higher C-charge at the same time as “unashamedly” expanding the £12.50-a-day ultra-low emission zone to the boundaries of the North and South Circular roads on October 25.
The C-charge was increased to £15 by Mr Khan as a condition of the Government’s first covid bailout for TfL last May, and to tackle rising levels of traffic in central London.
The £1.6bn bailout required him to “urgently bring forward proposals to widen the scope and levels” of the charge — though it did not say by how much.
Mr Khan told the LBC hustings yesterday that he was keen to return to “some sense of normality as the pandemic ends” in relation to the congestion charge.
He suspended the levy on March 23 last year to enable essential workers to drive to work during lockdown but reintroduced it on May 18 after car traffic was found to be six per cent above pre-lockdown levels, raising concerns about gridlock.
The latest figures from TfL show that 46,489 drivers paid the C-charge daily at the end of last year, about three-quarters of pre-pandemic levels.
It costs £110m to £130m a year to fund free travel for children and over 60s. About £43m of this is being covered this year by higher council tax bills, with the remainder due to come from the £15 C-charge.
A Labour spokeswoman said: “Government ministers made it a requirement of the [second TfL] funding deal [in October] that the temporary changes to the congestion charge remained in place, and they rolled this condition forward when they extended the funding deal in March.
“As covid restrictions are eased and travel patterns change, Sadiq will - if re-elected - have discussions with the Government about the best arrangements to have in place to support London’s economic recovery and to ensure it is a green and sustainable one.
“It is likely that temporary restrictions will need to remain in place until the autumn, whilst these discussions are conducted.”
Both the Greens and Lib-Dems favour replacing the congestion charge and Ulez with a system of “smart” road-pricing.
Tory candidate Shaun Bailey said he would also axe the £15 C-charge and return it to £11.50 on weekdays. He would also cancel the Ulez expansion.