The UK must redouble its efforts to fight coronavirus, Prime Minister Boris Johnson has said, as an extra 20 million people in England were plunged into the toughest Tier 4 lockdown restrictions.

On the day a vaccine from Oxford University and AstraZeneca was approved to tackle Covid-19, Mr Johnson said a new strain of the virus was “surging across the country” and immediate action was needed.

He told a Downing Street briefing that the Oxford vaccine and one from Pfizer were being rolled out, adding: “We are working as hard and as fast as we can to get the supplies to you.”

But he said: “We have to face the fact that we’ve got two big things happening at once in our fight against Covid – one’s working for us and one’s working against us.

“On the plus side, we have got two valid vaccines, and we’re racing to get them out – and on the bad side there is a new strain of the virus which is spreading much faster and surging across the country.”

Referring to new tier allocations announced by Health Secretary Matt Hancock, Mr Johnson said: “At this critical moment, with the prospect of freedom within reach, we’ve got to redouble our efforts to contain the virus

“No-one regrets these measures more bitterly than I do, but we must take firm action now.”

It came as a further 981 people had died within 28 days of testing positive for Covid-19 as of Wednesday, bringing the UK total to 72,548.

This is the highest daily figure reported since April 24, when 1,010 deaths were reported, but there is likely to be a lag in reporting deaths over the Christmas period.

Among the areas moving to Tier 4 are the Midlands, parts of the North East and North West and parts of the South West.

An additional 20 million people will move to the tightest restrictions, making a total of 44 million in Tier 4, or 78% of the population of England.

According to the Department of Health, between December 18 and 24, the weekly Covid-19 case rate in England rose to 402.6 per 100,000, a 32% increase on the previous week.

Some 14,915 patients have been admitted to hospital with Covid-19 in the past week, an 18% increase on the week before.

Earlier, Education Secretary Gavin Williamson said students in exam years will return to secondary schools a week later than planned, from January 11.

Other secondary and college students will go back full-time on January 18.

Primary schools where Covid-19 infection rates are the highest will not reopen for face-to-face teaching to all pupils as planned next week.

Responding to the fact that most of the country will now be in Tier 4, England’s deputy chief medical officer Professor Jonathan Van-Tam told the Downing Street press conference: “Unfortunately it is a pretty grim and depressing picture at the moment.”

But he said it will be known within the next few months what the impact is of vaccines on reducing severe illness in the population.

Mr Johnson said he hoped that by spring of 2021, many coronavirus restrictions would have receded.

He said: “If we’re right and the vaccination programme does have the positive effects that we think it can have, and I stress these are ifs, then clearly a lot of the non pharmaceutical interventions…will recede into the past.

“We’ll be able to do things very differently.”

The Prime Minister added that the public may need to carry on with “basic disciplines” such as washing hands and wearing masks “for a while after”.

Earlier on Wednesday, Mr Hancock said the approval of the Oxford vaccine by the Medicines and Healthcare products Regulatory Agency (MHRA) was a “great British success story” and 530,000 of doses will be available for rollout from Monday.

He told Sky News he was “highly confident that we can get enough vulnerable people vaccinated by the spring that we can now see the route out of this pandemic.”

The UK has ordered 100 million doses of the Oxford University vaccine, enough to vaccinate 50 million people.

The plan is to vaccinate all vulnerable groups first, with all adults eventually offered the jab.

All parts of the UK will receive the jab from Monday, with devolved administrations in Wales and Scotland saying they were ready to receive their allocation.

In Wales, health minister Vaughan Gething said vaccines were not an “instant fix” to the Covid-19 pandemic and urged people to continue to follow regulations to limit the spread of the virus.

Meanwhile, Dr June Raine, chief executive of the MHRA, said her team of scientists and clinicians had “very carefully and methodically and rigorously reviewed all the data on safety, on effectiveness, and on quality” relating to the vaccine.

She added: “No corners, whatsoever, have been cut.

“The safety of the public always comes first.”

Data published in The Lancet medical journal in early December showed the vaccine was 62% effective in preventing Covid-19 when given as two full doses, but also appeared to prevent any severe disease.

The MHRA has authorised two full doses of the vaccine, with the second dose given four to 12 weeks after the first.

It said the vaccine was up to 80% effective when there was a three-month interval between the first and second doses, according to further data that has yet to be published in a medical journal.

A first dose of the jab gives 73% effectiveness from three weeks after immunisation until a second dose at 12 weeks, according to the MHRA and the Joint Committee on Vaccination and Immunisation (JCVI).

Prof Van-Tam said giving a first dose followed by a second dose up to 12 weeks later “makes enormous sense to me as somebody who is public health trained.”

He said there are high levels of protection from both the Oxford and Pfizer vaccines after the first dose, though the second booster jab was still important.

Professor Wei Shen Lim, of the JCVI, said offering a first dose “will allow the greatest number of eligible people to receive a vaccine in the shortest time possible and that will protect the greatest number of lives”.

AstraZeneca chief executive Pascal Soriot told BBC Radio 4’s Today programme that deliveries will be ramped up “very rapidly” in the first and second week of January and up to two million doses a week.

Asked whether two million vaccinations per week was possible, Mr Hancock told Times Radio: “That’s absolutely deliverable by the NHS.”

The Oxford vaccine, which is being made in Oxfordshire and Staffordshire, can be stored in a standard fridge, unlike the Pfizer/BioNTech jab, which needs cold storage of around minus 70C.