Prime Minister Boris Johnson has ordered the closure of all travel corridors from Monday.

The move comes in an effort to protect the UK against new coronavirus strains, ending the quarantine exemption for arrivals from selected nations.

He told a Downing Street press conference: “It’s precisely because we have the hope of that vaccine and the risk of new strains coming from overseas that we must take additional steps now to stop those strains from entering the country.

“Yesterday we announced that we’re banning flights from South America and Portugal and to protect us against the risk from as-yet-unidentified strains we will also temporarily close all travel corridors from 0400 on Monday.

“Following conversations with the devolved administrations we will act together so this applies across the whole of the UK.”

The Prime Minister was appearing alongside Chris Whitty and Patrick Vallance during a Downing Street press conference on Friday night.

He confirmed all travel corridors will be suspended from 4am on Monday and anyone who wishes to travel to the UK must have proof of a negative Covid-19 test in the previous 72 hours.

Mr Johnson urged the British public to exercise caution despite the vaccine rollout and warned that the NHS is facing “extraordinary pressures”, having had the highest hospital admissions on a single day this week, and urged “this is not the time for the slightest relaxation of our national resolve”.

He said the country is involved in one of the fastest vaccination programmes in its history, but added: “It will be fatal if this sense of progress were now to breed any kind of complacency because the pressures on the NHS are extraordinary.

“On Tuesday we saw 4,134 new admissions to hospital on a single day – the highest at any point in this pandemic.

“There are now more than 37,000 Covid patients in hospitals across the UK and in spite of all the efforts of our doctors and nurses and our medical staff we’re now seeing cancer treatments sadly postponed, ambulances queuing, and intensive care units spilling over into adjacent wards.

“This is not the time for the slightest relaxation of our national resolve and our individual efforts. So please stay at home, please protect the NHS and save lives.”

He urged the public to remember that the disease can be spread not only by standing too close to someone in a supermarket queue but also by handling something touched by an infected individual.

Meanwhile, Chief medical officer Professor Chris Whitty praised the “enormous efforts by so many people” as the growth in the number of confirmed cases has slowed.

He told the press conference: “We were not sure this was going to be possible with this new variant, but this demonstrates with the actions everyone has taken we are now slowing this right down and we are hoping that in due course it will start to drop.”

But he warned that hospitalisations are still rising and this is set to continue.

Prof Whitty explained: "I’m afraid in the next week we do anticipate the number of people in the NHS and the number of deaths will continue to rise as the effects of what everyone has done take a while to feed through.”

The total number of jabs administered in the UK, including both first and second doses, is 3,678,180.