Taxpayers should preferably fund a new toll-free bridge over the River Severn, a former Government minister has said.
Mark Harper, who resigned as immigration minister last month, has written to the Highways Agency and asked it to examine future crossing options.
He insisted a long-term solution to ease severe traffic tailbacks at a free crossing near Gloucester, where the A40 meets the A48, would be for a bridge upstream of the Severn Bridge and Second Severn Crossing.
The Conservative MP for Forest of Dean said ideally a new crossing and the two Severn bridges would be toll-free.
But he asked the Government not to rule out using toll cash from the existing crossings if it meant a new bridge could be built within a couple of years rather than 20 years.
Welsh MPs criticised the idea, suggesting it could put a financial burden on people who live in South Wales.
Transport minister Robert Goodwill added it was Government policy for estuary crossings to be paid for by those who used it rather than out of taxation.
Speaking during a debate on the tolling on the Severn Bridges, Mr Harper told MPs: "In an ideal world I would like another crossing over the River Severn and I would prefer that to be paid for out of general taxation and not require either tolling on that crossing or indeed a continuation of tolling on the existing crossings."
Referring to Mr Goodwill, he went on: "What I don't want him to do is rule out looking at whether there should be some use of future tolling revenue to fund a third crossing.
"Because if I'm given the choice over crossing, I'll take the crossing, but if I'm told that I can't have a crossing for 20 years because it's unaffordable but I could have one in a year or two if we were able to use some toll revenue, that's a debate I want to have with my constituents.
"I want to see whether that would be a good trade-off, whether you look at the economic benefits to businesses to jobs and to economic activity and to relieving congestion.
"That may be a choice, that may be a balance that my constituents want to undertake.
"So I at least want the minister not to rule that out.
"I've written to the Highways Agency to ask them to look at some options for further crossings.
"I've also written to the Highways Agency to ask them to set out as well the future useful life of each of the Severn crossings - the second Severn crossing and the old Severn Bridge - to see how long they're likely to last for."
Mr Harper added: "I would prefer another crossing over the River Severn that doesn't have tolling, that doesn't require tolling on existing crossings.
"But I'm realistic to know, given the state of the public finances... there are going to be difficult decisions to be made and there is an argument to be made if you can have the infrastructure sooner by funding some of it from tolling that is a debate that is worth having and I want to put it on the table."
Welsh MPs were critical of the need for a third crossing, which they fear could have a negative impact on the two Severn bridges.
Paul Flynn, MP for Newport West, questioned if Mr Harper was suggesting there should be a bridge from "one thinly-populated part of England to another thinly-populated part of England" that placed a "financial burden" on people living in South Wales, who pay tolls on the main crossing.
Labour's Nia Griffith, MP for Llanelli, said she preferred Mr Harper's first suggestion that a third crossing would be paid for out of taxation from across the UK "rather than penalising one particular group of users".
Replying for the government, Mr Goodwill said: "Since 1945, it has been the policy of successive governments that crossings on estuaries should be paid for by the user rather than by the taxpayer.
"Successive governments have taken the view that tolls on all such crossings are justified because the user benefits from the exceptional savings in time and money that those expensive facilities make possible."
Mr Goodwill added on Mr Harper's proposal for a new bridge upstream, he said: "Certainly there are precedents of this around the country.
"I think of the Merseylink toll although those bridges are slightly closer together and, of course, many are considering that a new Lower Thames crossing could incorporate the existing tolls from the Dartford Crossing to make that particularly affordable."