France and Britain will reopen cross-border travel Wednesday after a snap 48-hour ban to curb the spread of a new coronavirus variant threatened UK supply chains.

Much of Europe swiftly banned British travellers and UK freight entering their nations after the discovery of a more transmissible variant of Covid-19 in Britain.

On Tuesday, dramatic images showed hundreds of lorries backed up in Dover, with British Prime Minister Boris Johnson facing growing pressure to resolve the deadlock even as the post-Brexit trade deal deadline loomed.

UK Transport Secretary Grant Shapps announced late Tuesday that Britain and France had settled on a protocol that "will see the French border reopen to those travelling for urgent reasons, provided they have a certified negative COVID test."

However, he urged lorry drivers not to head to the southern county of Kent in expectations of boarding a ferry or train.

French Transport Minister Jean-Baptiste Djebarri also confirmed that air travel, boats and Eurostar trains would "resume service as of tomorrow morning".

"French nationals, people living in France and those with a legitimate reason will have to be carrying a negative test," he said.

Despite the breakthrough in talks, congestion around the key southern port of Dover remains unlikely to recede in the short term.

Late Tuesday, the major British transit hub said it would reopen from midnight local time (2300 GMT) for travellers with a negative result.

A handful of passenger vehicles disembarked from two ferries in Calais early Wednesday, an AFP correspondent said, but port management said traffic was not expected to pick up until later.

Food shortage worries 

The measures imposed on hauliers have caused concern over shortages of some fresh food products over a Christmas period already marred by strict coronavirus restrictions.

More than 2,800 lorries remain stranded in the southern English county of Kent, unable to make the crossing to France, with drivers having spent a second night sleeping in their cabs.

As night fell on Tuesday, drivers of some 800 trucks parked at a nearby disused airport sounded their horns for more than half an hour in protest.

Despite the fresh agreement -- which will be reviewed on December 31 -- it is unclear when traffic will begin moving again.

The British transport ministry said: "All lorry drivers, irrespective of nationality, will require a lateral flow test."

In a statement, they added the test could detect the new Covid-19 variant "in around 30 minutes, rather than the 24 hours required after a PCR test".

The French Ministry of Transport said in a statement that all travellers from Britain would be required to present a negative Covid-19 test to their airline, ship or railway company less than 72 hours before departure.

French nationals, EU nationals or French residents who need to complete essential travel will be allowed to cross the border.

The European Union had called on members to facilitate transit and to lift other transport bans to avoid supply chain disruptions.

Johnson, criticised for his management of a pandemic that has caused nearly 68,000 deaths -- one of the highest death tolls in Europe -- has argued that the risk of transmission by lorry drivers was "really very low". 

According to the World Health Organization, transmission of this new variant is 40 to 70 percent higher.