MOTORISTS have avoided £33.6 million of fines because of glitches with the launch of Dartford Crossing's online payment system, a spending watchdog has found.

Highways England cancelled or decided not to issue penalty charge notices to some drivers because technical problems meant there was uncertainty over the records of which vehicles had failed to pay the correct fee, according to the National Audit Office (NAO).

Its report included in the crossing's 2015/16 accounts revealed the extent of taxpayer loss was between £4.6 million and £8.8 million.

This was because not all of the fines would have been recovered due to leniency towards first-time offenders, appeals and difficulty in obtaining the money.

Proceeds from the Dartford Crossing, which connects the M25 between Dartford in Kent and Thurrock in Essex, are sent to the Government for use on transport projects.

Toll booth cash payments were scrapped in November 2014 and replaced by the online Dart Charge scheme.

Enforcement was resumed during 2016 as the issues with the system were resolved.

Cars are charged up to £2.50 for each crossing and motorists who fail to pay within a day face being hit with a £70 fine.

Around 50 million vehicle crossings are made each year.

A Highways England spokesman said: "Dart Charge is the first scheme of its kind in the UK, and has been delivered successfully.

"This is the first set of accounts covering a full year of Dart Charge operation, and within the accounting periods there has been substantial progress in addressing these issues.

"Compliance with the scheme is high, and enforcement is being carried out effectively, fairly and appropriately."

The crossing's accounts show it generated an income of £161.2 million in 2015/16 - up from £99.8 million the previous year.

This was due to improved enforcement and increased usage.

Steve Gooding, director of motoring research charity the RAC Foundation, said: "In terms of reducing congestion and speeding up journey times, free-flow tolling has been a success.

"But it seems to have come at a financial cost with back-office system glitches costing taxpayers millions.

"Not for the first time there appears to have been problems relating to a government IT system."

He continued: "Is enough being done to ensure all drivers now using the crossing understand how and when they must pay so that few, if any, penalty charges need to be issued at all?"

AA spokesman Jack Cousens said: "The scale of fines issued shows that the current signage and information provided to drivers simply isn't adequate and must be addressed quickly.

"For many drivers, it seems the Dartford Crossing operator makes it as difficult as possible to pay the charge.

"Ever since the Dart Charge started, the AA has been calling for payment terminals to be made available at obvious locations, notably the motorway service area in Thurrock and the Eurostar terminal at Ashford.

"Despite the huge sums taken in fines, those payment terminals still haven't been set up."