Close to 10 million people have already used the tool to date, making sure that their vehicles comply with the new requirements.
Many of those who travel in the zone have already taken action to clean up their vehicles and help clean up London’s air.
More than 80 per cent of vehicles are now compliant, up from 39 per cent in February 2017 when the plans for the larger area were first announced.
Toxic air in London is a threat to life and can lead to a number of serious health conditions.
It contributes to thousands of deaths each year and is linked to heart disease and dementia as well as stunting the development of children’s lungs.
The expanded ULEZ is predicted to result in harmful nitrogen dioxide being reduced by around 30 per cent across the whole city.
The new zone will be 18 times the size of the current central area, which has seen toxic pollution slashed by half.
It will run 24 hours, seven days a week (except Christmas Day) and covers all areas within the North and South Circular. It is estimated that 100,000 cars, 35,000 vans and 3,000 lorries could potentially be affected by the tighter standards in the expanded area every day.
To prepare drivers and make them aware of the zone, TfL has run a far-reaching communications campaign.
More than a million letters have been sent to those seen driving in the area and more than 600,000 leaflets have been sent to residents living close to the boundary.
Four million emails have been sent to people on TfL’s customer database, and there has been an extensive advertising campaign spanning radio, TV, posters, press, social media and online.
Drivers have been supported in making the transition with the Mayor’s £61 million scrappage scheme.
To date, more than 12,000 older polluting cars, vans, minibuses and HGVs have been taken off the road or retrofitted.
TfL is also greening its own fleet with more than 500 zero-emission buses on the city’s streets and more than 4,000 iconic black cabs are now using electric.
The RAC's head of roads policy, Nicholas Lyes, said: “While the majority will be unaffected by the expansion of the Ultra Low Emission Zone, around a fifth of vehicles don’t comply, so it’s vital drivers of cars, small vans and motorbikes use the TfL checker before October 25 or be prepared to pay a £12.50 daily charge.
Drivers should also remember that the ULEZ, including the new expanded zone, operates 24 hours a day, seven days a week.”