The site has been hit by problems since yesterday when it told users its systems were "at capacity".

It also said its contact centre had been experiencing "exceptionally high demand" as drivers have sought to pay over the phone.

Trying to access the website on Tuesday leads would-be customers to a dead end with the message: "To manage high demand, you have been placed into a queue...Apologies for any inconvenience."

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Dozens took to Twitter to vent their frustrations that the website was down.

Broadcaster and podcast host Jemma Forte said she had "been trying to pay on and off" ever since using the crossing on Thursday.

She added: "Website is either not working or puts you in a queue which never gets anywhere."

Others claimed after managing to access payment options, they were unable to pay or that they were refused payment but their bank accounts had been debited regardless.

The Dart Charge applies daily between 6am and 10pm to most vehicles apart from motorcycles and those with disability exemptions.

A single car journey over the Queen Elizabeth II bridge, which connects Essex to Kent, costs those with an account £2, while large vehicles pay in excess of £5.

Those who forget or fail to pay the charge face an £70 fine but this is halved if paid within 28 days - or increased to £105 if not.

A National Highways spokesperson told Sky News: "The Dart Charge contact centre and website is still experiencing exceptionally high demand after the system updates made over the weekend.

"We are extending the payment period for crossings made since Thursday 27 July to allow everyone sufficient time to make payment once the system is functioning as normal."

They added that once the system is functioning as normal again, they would give road users sufficient time to pay for their crossing.