More than 1,500 lorries are stuck in Kent waiting to leave the UK as politicians thrash out a plan to reopen France’s border to trade and travel.
More than 40 countries have banned arrivals from the UK amid fears of a new coronavirus variant, and France shut its border for 48 hours on Sunday.
Home Secretary Priti Patel said 650 lorries are stacked up on the M20, with a further 873 at a lorry park.
The UK’s top scientist has warned the new variant is “everywhere”.
Sir Patrick Vallance added that more areas may need to enter tier four, the new toughest tier, to curb its spread.
In England, 17 million people are under tier four rules.
Wales has entered a new national lockdown, Scotland has tightened rules and both Scotland and Northern Ireland will begin national lockdowns on Boxing Day.
Almost every EU member state has now stopped travel from the UK amid fears over the virus mutation, and the EU is talking about how to form a united response.
Home Secretary Priti Patel said discussions were under way between the UK and France “to find a resolution” to the Channel disruption.
“You’ll hear later on today in terms of developments and updates,” she told BBC Breakfast.
France’s Europe minister Clément Beaune said any plans would be agreed by Prime Minister Boris Johnson and French President Emmanuel Macron and come into effect from Wednesday.
Ms Patel said potentially testing lorry drivers at ports was “part of the discussions”, and added: “Getting those tests up and running can happen relatively quickly.”
EU member states are understood to be pressing for UK arrivals to be tested for the virus before entering their countries.
The border disruption also affected passenger services – with many air, rail and sea services cancelled between the UK and France, as well as other countries.
Rail operator Eurotunnel said it hoped passengers would be able to travel between the UK and France from Wednesday or Thursday, if a solution is agreed.
British Airways said it would operate “a reduced and dynamic schedule” amid the uncertainty.
Meanwhile, the World Health Organization said there was “zero evidence at this point” that the new variant of coronavirus discovered in the UK causes “any increase in severity associated with” Covid-19.
It urged the public to continue with measures known to reduce the spread: hand washing, social distancing, and wearing face coverings.
At the scene in Dover: BBC reporter Simon Jones
Driving around Dover this morning, there are HGVs everywhere – on the side of the road, in lay bys and in car parks.
Lorry drivers are used to sitting in delays, and will often sleep in their cabs. But for those I’ve spoken to this morning, it’s the uncertainty that is the most difficult thing.
They don’t know how long this will go on for; they don’t know whether they will get home for Christmas.
Even if France does reopen the border today, this backlog will take some time to shift, especially if drivers have to be tested before crossing the Channel.
The Channel is a vital trade route, with about 10,000 lorries a day travelling between Dover and Calais at Christmas, largely bringing in the freshest produce.
Lorry driver Greg Mazurek from Poland, who is in Dover and has been in his cab for two days, told the BBC on Tuesday morning: “What can I say? I feel bad, really bad, terrible in fact. We know nothing, we don’t know if we can get home [to] our families for Christmas.
“If they implement testing here, maybe it will be a good idea. But we need to start now, to get there [by] Christmas Eve.”
According to the head of the Road Haulage Association, lorry drivers waiting to cross the Channel were offered just a single cereal bar each by Kent County Council on Monday.
Meanwhile, Shane Brennan, the head of the Cold Chain Federation which represents the UK’s temperature-controlled transport industry, said the number of vehicles stuck was worse than the government figures suggested, as lorries were “dispersed around southern England”.
Ms Patel said the numbers do “fluctuate”, and added there were welfare facilities and support available for hauliers at Manston Airport.
Queues on the M20 in Kent aren’t exactly unheard of, but the French decision to close the border is dramatic and has caused a lot of disruption.
Politicians on both sides of the Channel are hopeful they might be able to agree a way of getting things moving again before the end of the year.
But if that requires a massive expansion of testing for coronavirus at the border, that’s easy to say, far harder to do.
About 1,550 lorries crossed into the UK through the port on Monday but retailers warned of “serious disruption” without a resolution, with Tesco and Sainsbury’s saying some fresh produce such as lettuce and citrus fruits could run short.
But Mr Johnson maintained delays only affected a very small percentage of food entering the UK and supermarket supply chains were “strong and robust”.
Labour said spare capacity in the coronavirus testing system should be used to help deal with the situation at British ports.
The UK’s chief scientific adviser told the Downing Street briefing that further restrictions are likely to be introduced in more areas of England to control the new variant of Covid-19.
Sir Patrick Vallance said measures could “need to be increased in some places, in due course, not reduced”.
London and large swathes of south-east England were placed in the highest tier four restrictions over the weekend.