Two cases of another new strain of Covid-19 linked to South Africa have been identified in the UK, Matt Hancock said.

It comes as more of the east and south east of England will enter the toughest Tier 4 lockdown on Boxing Day, the Health Secretary has announced.

The rate at which coronavirus is spreading has increased, adding to pressure on ministers to impose Tier 4 lockdowns on even more parts of England.

The Cabinet's Covid operations committee met on Wednesday to consider the latest data on the spread of the virus.

Communities Secretary Robert Jenrick acknowledged "it may be necessary to take further action" to curb rising case numbers.

Health Secretary Matt Hancock is set to deliver an update on the latest developments in a Downing Street press conference.

The latest estimate of the R value, the average number of people someone with coronavirus infects, has increased to 1.1 to 1.3, up from 1.1 to 1.2 a week ago.

The number of new infections is growing by between 1% and 6% every day, up from 1% to 4% last week.

The current tier levels in England are due to be reviewed on December 30 but that could be accelerated due to fears about the spread of the new variant coronavirus, which appears to be transmitted more readily than previous strains.

Mr Jenrick told Sky News: "We keep this under review, we are constantly hearing from our scientific advisers about what we should do."

The new variant is "very concerning" and is "prevalent probably in most regions of the country", he acknowledged.

Following the meeting of the Covid operations committee a health official said: "Ministers have met today to assess what further action may be needed to address the rise in cases driven by the new variant.

"The Health Secretary will provide an update at a Downing Street press conference at 3pm."

Scientists have repeatedly warned that the relaxation of coronavirus restrictions on Christmas Day could lead to increased cases and, ultimately, deaths.

Mr Jenrick said if the plans needed to change due to the new variant "we won't hesitate to do so".

But later he told BBC Radio 4's Today programme that there will not be changes to the Christmas arrangements.

"We are not going to change people's plans 24, 48 hours ahead of Christmas," he said, but "the strong advice is to keep it small, to keep it short and therefore to be safe".

Genomic researchers have found that the new variant, which is said to be 70% more infectious than previous strains, has already spread around the UK, with cases identified in Wales and Scotland.

If changes are announced to England's tiers, areas with higher infection rates will be braced for tougher restrictions.

In East Sussex, Wealden is currently in Tier 2, while neighbouring Rother is in Tier 4. The rate of new cases in Wealden has jumped week-on-week from 153.0 per 100,000 people to 351.8.

In the Midlands the rate in Tier 3 Rugby has jumped week-on-week from 151.5 to 377.3, while in Tier 2 Redditch it has risen from 105.6 to 224.0.

In the North West, Burnley has seen its rate jump sharply from 309.3 to 446.5 and might be facing a move from Tier 3 to Tier 4.

Pendle is another candidate for Tier 4, where the rate has risen from 267.1 to 345.2.

Professor Neil Ferguson, a member of the Government's New and Emerging Respiratory Virus Threats advisory group (Nervtag), said he expected lockdown measures to help control the spread of the variant.

Prof Ferguson told the committee on Wednesday: "Schools are now shut, we are in a near-lockdown situation across the country, contact rates are lower over Christmas.

"I expect, though I hesitate to make any sort of predictions, we will see a flattening of the curve in the next two weeks.

"We will see at least a slowing of growth."

Meanwhile, tempers flared at Dover 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 5,000 HGVs are being held in Kent, with drivers being tested for Covid-19 before they are allowed into France.

There were reports of disturbances at Dover and at the lorry holding facility in Manston involving those waiting to cross the Channel.

One man was arrested for obstructing a highway in Dover.

In other developments:

- Scotland's First Minister Nicola Sturgeon apologised and said she has "no excuses" for breaking coronavirus rules after being photographed in a bar not wearing a face mask.

- Oxford's Professor Sir John Bell said he expected regulators to approve the vaccine developed by the university's scientists "just after Christmas".

- Former prime minister Tony Blair said the Government should focus on distributing initial doses of vaccine to as many people as possible without holding back supplies for a second jab.