Highways England has said its preferred route for a new Lower Thames Crossing is a tunnel connecting Gravesend, in Kent, to Tilbury, Essex.
However, Tory MP for Gravesham, Adam Holloway, said the government should instead build a new tunnel between Dartford and Thurrock.
He claimed there would be "carnage" if the M25 at Dartford was "not fixed".
"This is quite simply the worst stretch of road in the UK, and it has a huge impact on local residents," Mr Holloway told MPs during a parliamentary debate on Monday.
"There are entirely viable schemes, including a seven-mile tunnel under Dartford and Thurrock," he said.
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The Conservative MP for Dartford, Gareth Johnson, suggested Mr Holloway was in favour of "funnelling more traffic" towards the existing Dartford Crossing and in to the Dartford area.
He said: "Isn't it the situation that we should have more resilience, as we have across the rest of the Thames, so you have crossings at various different locations?
"The solution surely is to take traffic away and put the crossing east of Gravesend."
But Mr Holloway said the "Â£5bn opportunity to fix the M25 is about to be wasted," adding that it will soon be "too late to stop a plan that's going to result in another 30 years of misery on the M25".
He added: "Have a conversation about something to the east of Gravesend, or wherever it is, but let's not confuse two things.
"The problem is a disaster at Dartford and it is going to be a complete scandal."
Concluding the debate, transport minister John Hayes said more than 47,000 people had taken part in a consultation on the preferred option for the crossing and the government was currently analysing the results.
A proposed new road tunnel beneath the River Thames would lead to 30 years of "misery" on the M25, an MP has warned.