Suburban drivers are rushing to check if their car will be liable for the charge (Picture: PA)

An official website for drivers to check whether their car will be liable for London’s ultra-low emission zone (Ulez) charge has partly broken down when demand is expected to skyrocket.

Millions more people will have to start paying the £12.50 charge for driving to and from their homes or commuting by car from Tuesday.

This is because the zone is being doubled in size to cover outer London, instead of only the capital’s busiest central boroughs..

Since the charge applies only to older, more polluting vehicles, Transport for London has set up an online tool which shows whether a given vehicle qualifies.

Users enter a vehicle registration number and are told whether they need to pay the Ulez charge on that vehicle.

For some time on Monday morning, users were forced to queue, suggesting the service was overwhelmed by demand.

The backlog appeared to clear later in the day, but a message on the site now reads: ‘As some of our services are unavailable right now, our vehicle checker will look a little different and some of the usual features will not be available.’

The zone’s expansion has become a divisive issue in Westminster and across south-east England (Picture: PA)

It was not immediately clear which services were affected, though it was possible to confirm that a car was compliant.

The scheme’s expansion, ordered by mayor Sadiq Khan, survived a High Court challenge by several Greater London councils who opposed the plans.

The outer London boroughs of Bexley, Bromley, Harrow, and Hillingdon, along with Surrey County Council, opposed the planned extension to ULEZ, which will soon cover all of London’s boroughs.

The scheme’s lack of popularity was also blamed for Labour’s recent by-election loss.

Here’s a map of areas where the scheme is expanding to.

Areas in light green will be covered by the scheme from Tuesday (Picture: Metro)

Drivers will not be charged if they are parked within an ultra-low emission zone or on days when they do not drive.

A ‘day’ is counted as the 24-hour period from midnight to midnight, meaning drivers could be charged £25 for late-night journeys

Transport for London (TfL) has estimated that on an average day, about 160,000 cars and 42,000 vans that use London’s roads would be liable for the fee.

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Drivers in outer London are rushing to check if their car will be liable for the charge from Tuesday.