Longer customs checks at the UK border could lead to tailbacks up to 29 miles long, new research has predicted.
The study by Imperial College London found that adding just two minutes to each vehicle check could more than triple the length of queues, according to the BBC.
The government has repeated its desire to make future trade with the EU as “frictionless” as possible.
But researchers estimate that if additional customs checks are introduced, it will add around 10 minutes to queues at peak times for every additional minute that vehicles are checked.
Dover MP Charlie Elphicke told the BBC the research was evidence the UK needs a free trade deal with the EU.
He said: "The obvious and logical thing at the beginning is to have a no-tariff deal because that way trade continues to flow between Britain and the EU and everyone wins."
The research follows a warning from the head of the port of Calais, Jean-Marc Puissesseau, that mandatory customs and sanitary checks could cause 30-mile tailbacks at Calais and Dover and potential food shortages in the UK.