Five Conservative councils had in February launched legal action against the expansion, putting forward five grounds claiming that it is unlawful. In April, only two of those grounds were accepted by the court, with three refused.
But at a hearing on Friday, the coalition comprising the London boroughs of Bexley, Bromley, Hillingdon and Harrow, along with Surrey County Council, was told that two additional grounds for challenge - out of the three previously refused - would be considered as part of the judicial review.
It is thought that the review itself - which will effectively decide whether Mr Khan acted legally or illegally in the way he gave the go-ahead for the Ulez expansion - will take place on July 4.
A ruling against the mayor could potentially delay the August 29 expansion of the Ulez from its current boundary just inside the North and South Circular Roads.
According to Hillingdon Council, the two additional grounds for challenge - newly accepted by the court - are that there was an “unfair and unlawful consultation in relation to expected compliance rates in outer London” and, in relation to the scrappage scheme, “irrationality due to uncertainty and inadequate consultation”.
The two previously accepted grounds for challenge were that Mr Khan acted beyond his powers in expanding the Ulez by varying the existing scheme order rather than issuing a new charging order, and that he failed to consider including motorists living in the “buffer zone” on the edges of London in the £110m vehicle scrappage scheme.
Commenting on Friday, Nick Rogers, City Hall Conservatives transport spokesperson, welcomed the news that additional grounds have been accepted by the court.
He said: “From the evidence that has been uncovered, it’s obvious that Sadiq Khan does not have the legal basis to proceed with his Ulez tax plans, which take money from charities, small businesses and low income Londoners who cannot afford a new car.
“Sadiq Khan should do the right thing, stop work on his Ulez expansion, and explain his actions to the court."
A spokeswoman for Mr Khan said: “The Mayor has been clear that the decision to expand the Ultra Low Emission Zone London-wide was not an easy one. However, around 4000 Londoners a year die prematurely from air pollution.
“This is a health emergency and the Mayor is not prepared to stand by and do nothing while Londoners are growing up with stunted lungs and are more at risk of heart disease, cancer and dementia due to our toxic air.
“We note the Court’s decision and will continue to robustly defend action to expand the Ulez while continuing with preparations for expansion at the end of August.”
The Ulez requires drivers of older, more polluting vehicles to pay a £12.50 daily charge to use their cars.
Opponents of its expansion, which will mean it covers the whole of Greater London, say that it will have little impact on overall pollution levels but will hit people’s pockets during a cost-of-living crisis.
In an interview with the Times, published shortly before news of the court’s decision broke, Mr Khan pointed out that the five councils launching the legal action against the expansion are all Conservative-run.
“This is party politics,” the Mayor told the newspaper.
Councillor Colin Smith, the Tory leader of Bromley Council, said: “We are obviously delighted at the High Court’s latest decision, which has given further scope to the legal challenge we are mounting as it enables a broader range of legal questions to be posed.
"We are already witnessing widespread upset and uncertainty locally over the prospect of the Mayor’s threatened tax against motorists going ahead, due to the damage it will cause to local businesses, jobs and local care networks and anything which assists us in turning this outrageous money making scam away is clearly to be welcomed.
"Outer ‘London’ isn’t the same as inner London and never will be and every day which passes demonstrates ever more clearly that City Hall simply doesn’t understand how those of us in the cuter reaches need to live our lives due to the inferior transport networks and physically longer distances which people need to travel.
"Whilst the legal questions will be examined in court, there is still time for the mayor to draw back from expanding his unwelcome plans to extend his camera network to the outer London border ahead of the court case on 4th July and I once again call on him to do so for the wider good.
"If not, we travel on to ‘Independence Day’ bolstered by today’s decision in even greater hope than previously."