According to an investigation conducted by the broadcaster, the money has been collected since 2014, when toll booths from Essex and Dartford were first removed and substituted with online charges.
The crossing, first built in 1963, stretches 1,430 metres across the River Thames and is made up of the Queen Elizabeth II (QEII) Bridge and the Dartford Tunnel, connecting Essex and Kent via the M25.
In the past year, 55 million crossings were made during the charging hours that fall between 6am and 10pm.
Motorists driving cars can pay a one-off journey fee of £2.50, whilst vans and small lorries pay a toll fee of £3 and larger lorries are charged a fee of £6.
Dart Charge account holders can pay a reduced amount with a prepaid account, for anyone wishing to pay in advance for journeys made.
National Highways told the BBC that customers were “made aware” that the credit would be available on their accounts 12 months from the time of payment.
It added that customers with inactive accounts will be contacted “within 90 days” to notify them of their account being closed, and that customers with closed accounts would receive an “automatic refund” via their original payment method.
The highways authority confirmed that the system has now changed and that Dart Charge account holders from 2021 would now receive an automatic refund.
According to financial accounts for the Dartford Crossing road charging scheme between 2022 and 2023, it was revealed that £4 million of the £5.3 million collected under the scheme had been held by the Department of Transport.
The report further revealed that £300,000 had been refunded to users with a further £100,000 set aside for claims.
How accounts become dormant
According to the National Highways website, Dart Charge accounts can become dormant under the following circumstances:
- If the account doesn’t have a vehicle registration (number plate)
- If the account doesn’t have a valid payment method
- If the account doesn’t have enough money in it to pay for a crossing
- If the account doesn’t have a record of crossings made in a 12-month period
What to do if you think you have money in a dormant account
Dart Charge customers are being advised to contact online or by calling 0300 300 0120 to claim a refund.