An extra 800 military personnel are to be sent to Kent on Christmas Day to help clear a backlog of lorries waiting to cross to France.
About 4,000 lorries are still waiting to cross the English Channel after the French closed their border with the UK.
Drivers must test negative for Covid-19 before boarding a train or ferry.
The extra support will take the number of military personnel delivering testing to drivers in Kent to about 1,100.
French firefighters have been supporting the testing effort, while the Polish defence minister said in a tweet that a team of territorial army soldiers would be sent to Kent.
Transport Secretary Grant Shapps said that of the 2,367 drivers tested by 12:00 GMT on Christmas Eve, three have tested positive.
Ferries will continue to operate over Christmas, but Mr Shapps said it could take several days to clear the backlog.