Grants of up to £2,000 will now be made available to all Londoners who wish to scrap any car or motorcycle that is non-compliant with the zone's emissions standards.

While previously only child benefit recipients, low-income and disabled people were eligible for scrappage grants, from Monday 21 August all people in the capital with non-ULEZ compliant cars or motorcycles can apply.

The payment for vans will rise from £5,000 to £7,000, with small businesses and sole traders able to receive up to £21,000 in grants to scrap up to three vans.

However, the scrappage scheme is not retrospective - meaning those who have already paid for a new vehicle will not be reimbursed the grant.

The Conservatives described the development as "too little too late".

The concession, funded by £50m of City Hall reserves, comes after the Tories were able to hold on to Boris Johnson's former seat campaigning on an anti-ULEZ platform, which is due to be expanded to outer London at the end of the month.

The extra £50m takes the total value of the scrappage fund to £160m.

The ULEZ - which is already in place in central and inner London - charges motorists £12.50 a day to drive the most polluting vehicles in the boundaries it covers.

From 29 August, the zone will be extended up to the capital's borders with Buckinghamshire, Essex, Hertfordshire, Kent and Surrey.

The mayor has repeatedly stressed that 90% of cars seen driving in outer London on an average day are already ULEZ-compliant, but the expansion of the scheme has encountered fierce resistance in some areas due to the rising cost of living.

In the wake of the Uxbridge by-election result - which the Tories won by just 495 votes - a number of senior Labour politicians, including leader Sir Keir Starmer and deputy Angela Rayner, came on to the airwaves to denounce the policy.

In a direct rebuke to the Labour London mayor, Sir Keir told Sky News that his party lost the Uxbridge by-election because of the scheme's expansion as he urged Mr Khan to "reflect".

Mr Khan has stuck by the policy, citing the damaging effect of air pollution on Londoners' health.

Last week he was boosted by a High Court ruling which found the expansion to the capital's outer boroughs was lawful.

Under the extended scrappage scheme, charities will be able to receive up to £27,000 in grants to scrap up to three minibuses, while from Friday, increased grants will come into force for non-compliant vans and mini-buses.

Mr Khan, said: "I have always said that expanding the ULEZ to the whole of London was a difficult decision, and not one I took lightly - but it's a decision I remain committed to seeing through.

"I'm not prepared to step back, delay or water down vital green policies like ULEZ, which will not only save lives and protect children's lungs by cleaning up our polluted air but help us to fight the climate crisis.

"I have continued to listen to the concerns of Londoners over recent months, and today I can announce a huge expansion to the scrappage scheme that means that all Londoners with non ULEZ-compliant cars will now be able to get financial support to switch to greener, less polluting vehicles."

The mayor's intervention was welcomed by disability rights champion Dr Kush Kanodia, who said it was "great news for the disabled community and shows campaigns from disabled people can have a significant impact to change the policy in Greater London".

Tim Dexter, clean air lead at Asthma + Lung UK, said: "ULEZ is about reducing the number of polluting vehicles on the road and helping every Londoner breathe cleaner air, including the estimated 585,000 people living with asthma or chronic obstructive pulmonary disease living across London.

"Schemes like ULEZ are proven to reduce air pollution - a public health emergency contributing to 4,000 early deaths in London every year."

But Susan Hall, who will stand for the Tories against Mr Khan at the next mayoral election in 2024, said: "This is too little, too late from Sadiq Khan, who is facing mounting pressure from Londoners and his own party.

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"Thousands of families, small businesses and charities face financial ruin because of Sadiq Khan's ULEZ expansion, which will do next to nothing to improve air quality.

"If I am elected mayor, I will reverse this disastrous policy and replace it with a £50m fund to reduce air pollution without taxing people."

Keith Prince, City Hall's Conservative transport spokesperson, claimed it was an "act of desperation to appease members of his own party" but would not "go far enough to stop the damage his ULEZ expansion will do to Londoners".

"The best thing he could do is U-turn and adopt some policies that would actually clean the air, such as accelerating the move to zero-emission buses," he said.