Tough restrictions are required now to stop coronavirus “running out of control” in January due to the new variant of the virus, Boris Johnson has warned.

The Prime Minister told a Downing Street press conference that England was facing “considerable new pressures” from the mutant strain, which has led to harsher restrictions across the South East of the country.

He said that a tough tier system, community testing and rolling out the vaccine would be the approach to tackling the pandemic – but did not rule out a second national lockdown after Christmas.

It comes after analysis by the Office for National Statistics (ONS) found that around half of all new coronavirus cases in England could be the new variant.

Concerns over the mutant strain, which scientists have concluded spreads more rapidly, mean millions of people in England will join those already under lockdown conditions from Boxing Day.

Asked if he could rule out a national lockdown after Christmas, Mr Johnson said: “Obviously we face very considerable new pressures, particularly from the new variant and the speed with which that’s been spreading.

“We believe that we’re going to have to get through this tough period now with, as I say, as I have said many times, very tough restrictions, with tough tiering.

“You will have seen what has been announced over the last day or so about that and, much as I regret that, I do think it is necessary for us to grip this virus now, to stop it running out of control in January.

“Because we need to buy ourselves time to get the vaccine into as many arms of the elderly and vulnerable as we can. That is the real way in which we will defeat the virus.

“So, it’s tough tiering, community testing and rolling out the vaccine, and we’re going to continue with that approach.”

He added: “I know that it’s been very, very tough over the last few weeks and, I must tell people, it will continue to be difficult.”

Official figures showed a further 574 people had died within 28 days of testing positive for Covid-19 as of Thursday, while there had been a further 39,036 lab-confirmed cases of coronavirus in the UK.

During his address on reaching a post-Brexit deal with the European Union on Thursday, Mr Johnson said that almost 800,000 people had now been vaccinated.

New figures published by the Department of Health and Social Care on Thursday said that 616,933 people in the UK had received the first dose of the Pfizer and BioNTech vaccine between December 8 and December 20.

Meanwhile, the ONS said an estimated 645,800 people in private households in England had Covid-19 between December 12 and 18 – the equivalent of around 1.18% of the population, or one in 85 people.

In London, 68% of positive cases from December 14 to 18 were estimated to be genetically compatible with the new variant, while in eastern and south-east England the estimate is 65%.

For England as a whole, the statistics agency estimates that 49% of new cases could be the mutant strain that resulted in the creation of the new Tier 4 restrictions.

Following disruption which has left thousands of lorry drivers stranded in Kent, Transport Secretary Grant Shapps said on Christmas Eve that ferries from Dover to Calais would run on Christmas Day and Boxing Day.

French firefighters and British military are working with NHS Test and Trace to test thousands of waiting hauliers, who must return a negative test within the past 72 hours to make the crossing.

Shortly after 1pm on Thursday, Mr Shapps said some 2,364 lorry drivers waiting to leave had returned negative coronavirus tests, while three had tested positive.

More than 1,000 lorries have left the UK since Wednesday evening via the Eurotunnel, according to the Road Haulage Association, with around 2,000 more expected to be able to leave by the end of Thursday.

In other developments:

– London’s rate of new cases of Covid-19 has trebled in just two weeks, according to the latest weekly surveillance report from Public Health England.

– NHS Test and Trace figures show that 34.1% of people tested at an “in-person” site in the week ending December 16 received their result within 24 hours, downing from 59.8% the previous week.

– China’s foreign ministry said it would suspend flights to and from the UK, joining a list of nations who have imposed travel bans in light of the discovery of the variant.

– New York City mayor Bill de Blasio announced that authorities would personally visit all travellers from the UK to ensure they are isolating.

– The UK announced a travel ban on South Africa amid concerns over another new strain of Covid-19.