Patrick McLoughlin said the change would be a boost to small businesses around the Dartford-Thurrock crossing as it includes privately registered vans for the first time.

Tory MPs Jackie Doyle-Price (Thurrock) and Gareth Johnson (Dartford) were highlighted by the Transport Secretary for their campaigns on the issue.

Speaking during transport questions in the Commons, Mr McLoughlin said: "I am announcing today important changes to the discount scheme which will help local people who use the Dartford-Thurrock crossing following a persuasive campaign by the MPs for Dartford and Thurrock.

"From March 2014, those registered on the scheme will be able to make unlimited trips over the crossing for just £20 a year.

"For the first time, we will include privately registered vans, offering a welcome boost to small businesses."

During the day, the cash charge for a car is £2 and £2.50 for a two-axle goods vehicle. Discounts are available for people using a "Dart-Tag".

The east London crossing is free between 10pm and 6am.