A group of five Conservative-led councils have lost their High Court challenge against Mayor of London Sadiq Khan’s plans to expand the capital’s ultra low emission zone (Ulez).

The outer London boroughs of Bexley, Bromley, Harrow and Hillingdon along with Surrey County Council launched legal action in February over the Labour mayor’s proposals to extend Ulez beyond the North and South Circular roads.

Mr Khan described the judgment as a “landmark decision” and said he will press ahead with the Ulez expansion on August 29 as planned.

He said: “The decision to expand the Ulez was very difficult and not something I took lightly, and I continue to do everything possible to address any concerns Londoners may have.”

Ian Edwards, leader of Hillingdon Council, said he was “hugely disappointed” by the ruling and pledged to “continue our fight” through Parliament and at next year’s mayoral election.

He added: “I am proud that we had the courage and conviction to stand up for our residents and businesses.”

Colin Smith, leader of Bromley Council, said the decision “cannot be disguised as anything other than bitter disappointment for motorists”.

RAC head of roads policy Nicholas Lyes called for “additional support given to certain keyworkers” living in the capital and in neighbouring counties to switch to cleaner vehicles “as affordably as possible”.

Hirra Khan Adeogun, co-director of climate charity Possible, said: “It’s fantastic that we can get on with the expansion of the Ulez, which is sorely needed to tackle our overreliance on cars and improve air quality in the capital.”

At a hearing earlier this month, the local authorities’ lawyers said the mayor lacked the legal power to order the expansion of the zone by varying existing regulations and argued that there was an “unfair and unlawful” approach to collecting views on the plans.

The mayor’s legal team rejected the bid to quash his November 2022 decision to extend Ulez to all of London’s boroughs, arguing the move was “entirely lawful” and that “ample information” was provided for a “fair consultation”.

In a ruling on Friday, Mr Justice Swift dismissed the councils’ case.

Giving a summary of his findings, the judge said: “I am satisfied that the mayor’s decision to expand the Ulez area by amendment of the present road charging scheme, rather than by making an entirely new … scheme, was within his powers.”

The judge added that, having “carefully considered” the consultation process, he was satisfied that enough information was given for people who wished to respond to provide “informed responses”.

The councils had also challenged plans for a £110 million scheme to provide grants supporting the scrapping of non Ulez-compliant vehicles, arguing they were unlawful because a “buffer zone” for “non-Londoners” affected by the extended charging zone was not considered.

Mr Justice Swift said the consultation on the scrappage scheme was “not in depth”, but was “lawful”.

If it goes ahead, the extended Ulez will see drivers in outer London pay a £12.50 daily fee from August 29 if their vehicles do not meet the required emissions standards.

The new borders will reach Buckinghamshire, Essex, Hertfordshire, Kent and Surrey.

Friday’s ruling comes in the wake of last week’s Uxbridge and South Ruislip parliamentary by-election, where Labour’s failure to win ex-prime minister Boris Johnson’s seat was blamed on concerns around the expansion of Ulez.

From Monday, access to the mayor’s £110 million scrappage scheme will be extended to include all families in receipt of child benefit in London and every small business in the capital if they have a non-compliant vehicle.

At the end of last month some £68 million remained available through the programme.