Boris Johnson has announced strict coronavirus restrictions for England over Christmas, with London, the South-East and East also placed under a new tier 4.

The announcement made at a Downing Street Press conference on Saturday comes amid fears a new variant of Covid-19 is spreading more rapidly across parts of the country.

The prime minister revealed that the variant could be “up to 70% more transmissible” than the original variant.

Chris Whitty, England’s chief medical officer, said there is no evidence the new variant of the virus is more deadly or will affect the vaccine, but it can spread more quickly.

The government had previously told people three households would be allowed to mix for five days between December 23 and December 27, however that has now changed.

People living in tier 4 areas will be banned entirely from mixing with households over Christmas.

In all other areas of England, Christmas bubbles will be permitted on Christmas Day only.

Under the new tier 4 rules, which will come into force from Sunday, people will be ordered to stay at home by law and non-essential retail will shut.

In tier 4 areas, one person will only be allowed to meet one other person not in their household and it must be outside. Travel will be banned into and out of tier 4 areas.

The new rules will be reviewed after two weeks.

Tier 4 restrictions will apply in all current tier 3 areas in the South-East, covering Kent, Buckinghamshire, Berkshire, Surrey (excluding Waverley), Gosport, Havant, Portsmouth, Rother and Hastings.

It will also apply in London (all 32 boroughs and the City of London) and the East of England (Bedford, Central Bedford, Milton Keynes, Luton, Peterborough, Hertfordshire, Essex (excluding Colchester, Uttlesford and Tendring).

Mr Johnson, who on Wednesday said that spending Christmas with friends and family would be “inhuman”, said he was taking just that action now “with a very heavy heart”.

I know how much emotion people invest in this time of year, and how important it is, for instance, for grandparents to see their grandchildren, for families to be together,” he said. “So I know how disappointing this will be.

“But we have said throughout this pandemic that we must and we will be guided by the science. When the science changes, we must change our response.”