The RAC, which carried out the research, said the expansion of the zone – due to start from 29 August this year – will have a “massive financial impact on motorists and businesses”.

The news comes a day after Transport for London (TfL) claimed that nine out of 10 cars seen driving in outer London on an average day already meet the ULEZ standards, so would not be liable for the charge.

TfL also claimed that many drivers are switching from older, more polluting vehicles ahead of the expansion.

The controlled zone is currently limited to the area within London’s North and South Circular roads, but Mayor Sadiq Khan has moved to expand it to cover the whole of the capital in an effort to improve air quality for all residents.

Most diesel cars registered before September 2015 and petrol cars registered prior to January 2006 are liable for the ULEZ charge.

Driver and Vehicle Licensing Agency (DVLA) figures obtained by the RAC show that 691,559 licensed cars in the whole of London fall into one of those categories.

This does not take into account other vehicle types, such as vans and lorries, or the many vehicles which enter London from neighbouring counties such as Essex, Hertfordshire, Surrey and Kent.

Nicholas Lyes, RAC head of roads policy, said: “Cleaning up London’s air should undoubtedly be a priority, but the sheer number of vehicles that don’t meet ULEZ emissions standards in Greater London suggests there will be a massive financial impact on motorists and businesses through having to fork out £12.50 every day they drive in the zone.

“We desperately need more co-ordination between the mayor and the government to help small businesses, tradespeople, NHS staff and carers who have no choice but to drive into the expanded ULEZ for work purposes from outside Greater London.

“Consideration should also be given to those who work at night when public transport is greatly reduced in the outer boroughs.”

TfL is running a scrappage scheme for vehicles that do not comply with the ULEZ standards.

It includes payments of up to £2,000 for eligible drivers such as those on low incomes or the disabled scrapping a car and up to £9,500 for charities, sole traders and small businesses scrapping or retrofitting vans and minibuses.

Lyes urged Khan to consider delaying charges by a year for certain key workers, or introducing a scheme whereby TfL partners with a leasing company to provide discounted ULEZ-compliant vehicles to small businesses and traders.

“Changing to a compliant vehicle at such short notice simply won’t be something many will be able to afford, especially during a cost-of-living crisis and at a time when second-hand car prices are so high”, Lyes said.

“We need more creativity from London’s mayor and his team to help people out as the current scrappage scheme is akin to using a plughole to drain an Olympic-sized swimming pool. It’s simply not big enough for the scale of the job.”

Speaking on Thursday, Khan said that the aim of the ULEZ is to “get the most polluting vehicles off our roads in order to protect both the health of Londoners and our environment”.

He continued: “People, businesses and charities understand the impact of air pollution on health and are preparing for the change. It’s now just one in 10 cars seen driving in outer London that aren’t ULEZ compliant – a fantastic result.

“We expect the number of compliant vehicles to go up even more as people prepare for the expansion, but we know there is more to do to ensure every Londoner can breathe cleaner air.

“For drivers of the very few non-compliant vehicles, I have launched the biggest scrappage scheme ever.”

TfL’s £110m scrappage scheme was announced in January this year, offering Londoners receiving certain means-tested benefits and non-means-tested disability benefits cash grants of up to £2,000 to scrap non-compliant cars or motorcycles. They can also choose to receive a higher-value package comprising up to two free annual bus and tram passes and a lower cash grant.

The ULEZ switch has been compounded by the challenge of sourcing affordable compliant vehicles, with a marked shortage of suitable second-hand vehicles. According to an AutoTrader review carried out in February, only 5,150 ULEZ-compliant cars priced below £5,000 were up for sale in London.

Meanwhile, TfL is facing a legal challenge to its ULEZ expansion plans. Five Conservative-run councils – Bexley, Bromley, Harrow and Hillingdon and Surrey County Council – have formed a coalition to mount a legal challenge against the plans. Their argument alleges that the scheme fails to comply with statutory requirements and that the proposed scrappage scheme was not consulted upon.

The RAC, which carried out the research, said the expansion of the zone – due to start from 29 August this year – will have a “massive financial impact on motorists and businesses”.

The news comes a day after Transport for London (TfL) claimed that nine out of 10 cars seen driving in outer London on an average day already meet the ULEZ standards, so would not be liable for the charge.

TfL also claimed that many drivers are switching from older, more polluting vehicles ahead of the expansion.

The controlled zone is currently limited to the area within London’s North and South Circular roads, but Mayor Sadiq Khan has moved to expand it to cover the whole of the capital in an effort to improve air quality for all residents.

Most diesel cars registered before September 2015 and petrol cars registered prior to January 2006 are liable for the ULEZ charge.

Driver and Vehicle Licensing Agency (DVLA) figures obtained by the RAC show that 691,559 licensed cars in the whole of London fall into one of those categories.

This does not take into account other vehicle types, such as vans and lorries, or the many vehicles which enter London from neighbouring counties such as Essex, Hertfordshire, Surrey and Kent.

Nicholas Lyes, RAC head of roads policy, said: “Cleaning up London’s air should undoubtedly be a priority, but the sheer number of vehicles that don’t meet ULEZ emissions standards in Greater London suggests there will be a massive financial impact on motorists and businesses through having to fork out £12.50 every day they drive in the zone.

“We desperately need more co-ordination between the mayor and the government to help small businesses, tradespeople, NHS staff and carers who have no choice but to drive into the expanded ULEZ for work purposes from outside Greater London.

“Consideration should also be given to those who work at night when public transport is greatly reduced in the outer boroughs.”

TfL is running a scrappage scheme for vehicles that do not comply with the ULEZ standards.

It includes payments of up to £2,000 for eligible drivers such as those on low incomes or the disabled scrapping a car and up to £9,500 for charities, sole traders and small businesses scrapping or retrofitting vans and minibuses.

Lyes urged Khan to consider delaying charges by a year for certain key workers, or introducing a scheme whereby TfL partners with a leasing company to provide discounted ULEZ-compliant vehicles to small businesses and traders.

“Changing to a compliant vehicle at such short notice simply won’t be something many will be able to afford, especially during a cost-of-living crisis and at a time when second-hand car prices are so high”, Lyes said.

“We need more creativity from London’s mayor and his team to help people out as the current scrappage scheme is akin to using a plughole to drain an Olympic-sized swimming pool. It’s simply not big enough for the scale of the job.”

Speaking on Thursday, Khan said that the aim of the ULEZ is to “get the most polluting vehicles off our roads in order to protect both the health of Londoners and our environment”.

He continued: “People, businesses and charities understand the impact of air pollution on health and are preparing for the change. It’s now just one in 10 cars seen driving in outer London that aren’t ULEZ compliant – a fantastic result.

“We expect the number of compliant vehicles to go up even more as people prepare for the expansion, but we know there is more to do to ensure every Londoner can breathe cleaner air.

“For drivers of the very few non-compliant vehicles, I have launched the biggest scrappage scheme ever.”

TfL’s £110m scrappage scheme was announced in January this year, offering Londoners receiving certain means-tested benefits and non-means-tested disability benefits cash grants of up to £2,000 to scrap non-compliant cars or motorcycles. They can also choose to receive a higher-value package comprising up to two free annual bus and tram passes and a lower cash grant.

The ULEZ switch has been compounded by the challenge of sourcing affordable compliant vehicles, with a marked shortage of suitable second-hand vehicles. According to an AutoTrader review carried out in February, only 5,150 ULEZ-compliant cars priced below £5,000 were up for sale in London.

Meanwhile, TfL is facing a legal challenge to its ULEZ expansion plans. Five Conservative-run councils – Bexley, Bromley, Harrow and Hillingdon and Surrey County Council – have formed a coalition to mount a legal challenge against the plans. Their argument alleges that the scheme fails to comply with statutory requirements and that the proposed scrappage scheme was not consulted upon.