Rachel Canning was just about to take her son to school when the doorbell rang at her east London home.

There, on the porch, was a bailiff acting on behalf of the Dartford Crossing seeking hundreds of pounds over allegedly unpaid fees for the £2.50 toll, known as the Dart Charge.

Rachel is one of numerous people who claim to have faced “intimidation” and “harassment” by debt collectors over Dart Charge fines they claim were issued in error.

Some drivers who use the arterial bridge – connecting M25 stretches in Kent and Essex across the River Thames – have told the BBC they have faced account problems and hefty penalties.

National Highways, which oversees Dart Charge, has defended its handling of the cases and says it is working hard to “address customer concerns”.

Despite having an automated top-up account to cover the crossing fee, Rachel, who lives in Hornchurch, received six penalty notices in the preceding months.

Four fines were overturned. But when she challenged the other two – which had not appeared on her online account – she received no response from Dart and assumed they too were cancelled.

Then, on 20 June, she received a “notice of enforcement” from the Dart contractor, CDER Group, demanding £385 in relation to those two penalties.

Within a week, and despite challenging the fines and sending evidence to the Traffic Enforcement Centre (TEC), a bailiff arrived demanding £620 and threatening to clamp her car if she did not pay.

The experience left her son “very upset”, she says.

“The guy was quite abrupt, quite pushy, quite rude.”

Doorbell camera footage shows Rachel telling the bailiff the fines were being challenged and showing him her completed online forms.

“I spent five hours going between Dart Charge, the TEC and CDER Group to see what my options were,” she says. “None of them would take responsibility.”

The bailiff continued contacting her.

“He was harassing me the whole time, texting me, phoning me,” she says, claiming he told her every text he sent and phone call he made would be added to her debt.

Finding his behaviour “very threatening” and “intimidating”, Rachel paid up to make it stop.

Although she has since had £620 refunded, she has not received an apology.

CDER Group, which is one of three enforcement firms contracted by Dart Charge, says it did not capture her son on body worn video.

A spokesperson said that when an agent is assigned to a case their job is “to execute a warrant by full payment or removal of goods” which involves making “further contact with the debtor” until payment is made.

Aneta Wasilewska can see the Dartford Crossing from her flat in Grays, Essex.

Despite signing up to the resident discount scheme, which allows 50 free crossings a year and 20p per crossing thereafter, she went 20p into the red in July last year.

Her account was then closed without her knowledge.

She unwittingly racked up 39 fines which did not arrive until late November.

In March 2024 Dart Charge revoked the fines and emailed her – she now had seven days to pay £97.50 for the unpaid crossings.

Aneta did not receive the email because she was at a family funeral in Poland.

Efforts to resolve the matter with Dart Charge on her return failed.

Then came the CDER Group bailiff, who visited on 1 Jun saying she owed £7,800 and her car would be taken if she did not pay some money.

She paid £1,500 by card and agreed a payment plan of £500 a month.

Aneta says the situation caused “huge stress and anxiety”.

Her MP Jen Craft stepped in and wrote to National Highways. Within a week the fines and bailiff fees were cancelled.

But Aneta says she “never received an apology” from Dart.

CDER Group says it has reviewed the case and refunded her a further £290.

Bailiffs for the Dart Charge have collected £112m from 2.3m penalty notices in the past five years, figures obtained by the BBC reveal.

In 2023, the year in which Dart Charge switched its private operator, one in five fined drivers were referred to bailiffs.

During the first nine months of 2024, more than 2.7 million fines were issued by Dart Charge and 423,000 cases passed to enforcement firms – a higher number than in any of the previous five years.

Enforcement agency fees are set by law and state how much can be charged at each stage of the process.

Despite having an automatic top-up account for commutes between Kent and London, firefighter Andy Coote’s Dart Charge problems lasted more than ten months.

He was initially unaware he had received any fines because, for personal reasons, his post was being redirected to his daughter’s house.

By early May, he realised he had 34 fines. He paid them and contacted Dart Charge to ensure there were “no more in the system”.

But two days later he received an enforcement notice from CDER Group demanding £875 for 10 unpaid PCNs.

Two more penalties followed and, along with bailiff fees, Andy was told he owed £2,500.

He set up a monthly payment plan to try and clear the bill.

Andy, who admits he is not “good with computers”, says his boss was “amazing” and took time out to help him challenge each of the outstanding fines.

The stress of the Dart fines was “10 times more” stressful than his experiences as a firefighter, he says.

He accuses the CDER Group of using “intimidating” practices.

“I used to get four or five texts a day, the first one normally being at 06:00,” he says, adding the messages would warn him of “outstanding finances”.

“Then 15 minutes later the same thing, you get that four times a day, every day,” he adds.

CDER Group says it received “10 separate instructions” from Dart Charge to enforce warrants on Mr Coote which contributed to the number of letters and texts he received.

National Highways says in each of the cases highlighted the person either did not have an active account when they made the crossing, or the payment method on the account had not been updated, which led to the penalties.

A spokesperson said “almost 95% of crossings are paid on time” adding that “enforcement agents are only used as a last resort”.

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