Money from planned toll increases at the Dartford Crossing will not be ring-fenced to fund improvements at the site, despite previous assurances.
Under the government's Spending Review plans, charges for cars could rise from £1.50 to £2 in 2011 and £2.50 in 2012.
When transport minister Mike Penning was asked in October if the extra cash would be ring-fenced for crossing improvements, he replied: "Absolutely".
He has now said the money could be spent on other transport improvements.
'Disappointed but realistic'
The Conservative MP said: "That is the law, that is the legislation that's what I inherited when I became new minister six months ago.
"But what I'm saying is that the amount of money we're going to spend at Dartford is vastly in excess of what we are actually going to be taking at Dartford.
"So if you look at the investment in free-flow tolling, the removing of the barriers and the development costs of a new crossing in that part of the world, that is going to cost a lot more money than the 50p increases."
He added: "What is the point of ring-fencing something when I need more money.
"This is not owned by Essex and Kent and I know that feelings are strong down there but this is a piece of national infrastructure."
According to the DfT, the crossing tolls bring in about £40m in profit each year.
The proposed increases in tolls are subject to consultation.
Jeremy Kite, the leader of the Conservative-controlled Dartford Borough Council, said: "Quite frankly it's much more important to me that the crossing is not sold, much more important that the toll plaza is shut.
"Of course I have an ideal shopping list but I'm realistic [enough] to know that we have had a series of victories over the Dartford Crossing."
The Dartford Tunnel and Queen Elizabeth II bridge cross the River Thames between Dartford and Thurrock, forming a link in the M25 motorway, carrying about 150,000 vehicles a day.