Millions more people will be under the toughest coronavirus restrictions from Boxing Day as the UK implemented a travel ban on South Africa amid concerns over another new strain of Covid-19.

Health Secretary Matt Hancock warned the “highly concerning” new variant is believed to be more transmissible than the mutant strain that resulted in the creation of the new Tier 4 restrictions.

It is believed to be behind an increase in cases in South Africa, and has been discovered in two people in the UK thought to be contacts of those who travelled between the two countries in the last few weeks.

From 9am on Christmas Eve, visitors arriving into England who have been in or travelled through South Africa in the previous 10 days will not be permitted entry and direct flights will be banned, the Department for Transport said.

The ban excludes cargo and freight without passengers, and also does not include British and Irish nationals, visa holders and permanent residents, who will be able to enter but are required to self-isolate for 10 days along with their household.

Any exemptions usually in place – including for those related to employment – will not apply and passengers arriving in England from South Africa after 9pm on Wednesday cannot be released from self-isolation through Test to Release.

At a Downing Street press briefing on Wednesday afternoon, Mr Hancock said: “This new variant is highly concerning because it is yet more transmissible and it appears to have mutated further than the new variant discovered in the UK.”

Elsewhere, New York City Mayor Bill de Blasio announced that, due to a variant coronavirus in the UK, authorities would personally visit all travellers from the UK to ensure they are in quarantine.

“We’re going to have sheriff’s deputies go to the home or hotel of every single traveller coming in from the UK,” he told a press conference on Wednesday.

It comes as more than 40% of England’s population are settling in for lockdown conditions from Boxing Day after a further six million people were placed under Tier 4 restrictions.

Mr Hancock said the UK’s variant coronavirus was spreading at a “dangerous rate” as he announced the measures, which include tough restrictions on mixing with people and the closure of non-essential shops.

The changes were made as Government figures showed a further 744 people were reported to have died within 28 days of testing positive for Covid-19, the highest such figure since April 29 during the first peak of the virus.

There were a further 39,237 lab-confirmed cases of coronavirus as of 9am on Wednesday, the highest figure reported on a single day throughout the whole pandemic – although this is in part due to much wider testing.

Areas moving to Tier 4 from Boxing Day are: Sussex, Oxfordshire, Suffolk, Norfolk and Cambridgeshire, those parts of Essex not yet in Tier 4, Waverley in Surrey and Hampshire – including Portsmouth and Southampton but with the exception of the New Forest.

Tier 4 restrictions include a warning to stay at home, a limit on household mixing to two people outdoors and force the closure of many shops, hairdressers and gyms.

The measures come on top of Tier 3 restrictions such as the closure of pubs and restaurants except for takeaways and deliveries.

Bristol, Gloucestershire, Somerset including the North Somerset council area, Swindon, the Isle of Wight, the New Forest and Northamptonshire as well as Cheshire and Warrington will all be escalated to Tier 3.

Cornwall and Herefordshire move from Tier 1 to Tier 2.

The changes mean 24 million people will now be in Tier 4, or 43% of the population of England.

Northern Ireland confirmed a case of the new Covid-19 variant that was first detected in Great Britain on Wednesday evening.

Meanwhile, tempers flared in Kent as the French reopened the border to allow lorries to cross the Channel for the first time since emergency restrictions were imposed in response to the new variant.

More than 6,000 HGVs were being held in the county, with drivers being tested for Covid-19 before they are allowed to travel to France.

The Transport Secretary called for “patience” and said work continues to “get traffic rolling”.

While France eased its travel restrictions, Brazil has become the latest country to implement a ban on flights from the UK.

The Brazilian government announced late on Wednesday it was temporarily prohibiting flights that either originated from or passed through the UK in response to the emergence of the Covid variant.

Under the rules, which come into effect from Friday, foreigners who have been in the UK in the last two weeks will also be barred from boarding Brazil-bound flights.