Leeds news Live: Why lockdowns cannot end early due to more deadly Covid strain

Boris Johnson has appealed to people to stay home and follow the rules after he revealed the new variant may be associated with “a higher degree of mortality”.

He said the Government could have to bring in further restrictions on travel following a warning that other new variants found in South Africa and Brazil may be more resistant to the vaccines that have been developed.

Health Secretary Matt Hancock said in a private meeting with businesses: "There is evidence in the public domain, although we are not sure of this data so I wouldn't say this in public, but that the South African variant reduces by about 50% the vaccine efficacy."

Meanwhile, the British Medical Association has reportedly written to chief medical officer for England Professor Chris Whitty calling for the gap between doses of the Pfizer/BioNTech vaccine to be reduced to six weeks.

The private letter, seen by the BBC, said the current plans of people waiting up to 12 weeks for a second dose – which Health Secretary Matt Hancock said is supported by data from an Israeli study – are “difficult to justify”.

It said: “The absence of any international support for the UK’s approach is a cause of deep concern and risks undermining public and the profession’s trust in the vaccination programme.”

At a sombre No 10 news briefing on Friday, the Government’s chief scientific adviser Sir Patrick Vallance said early evidence suggested the new UK variant could increase mortality by almost a third in men in their 60s.

His warning followed a briefing by scientists on the Government’s New and Emerging Respiratory Virus Threats Advisory Group (Nervtag) which concluded there was a “realistic possibility” that it was associated with an increased risk of death.

It was already known that the new variant was up to 70% more transmissible than the original – leading to a tightening of restrictions across the UK from late December onwards.

Rowland Kao, professor of veterinary epidemiology and data science at the University of Edinburgh, said the latest findings suggested it was responsible for the “unexpectedly high” numbers of hospital admissions, especially around London.

“While the recent results showing declining case numbers is good news, and suggest that the variant is controllable via existing measures, these results on deaths imply that burden in hospitals will continue to be high requiring a more prolonged period of restrictions,” he said.

Professor Sir Mark Walport, a former government chief scientific adviser and a member of the Scientific Advisory Group for Emergencies (Sage), said even stricter measures may be needed if cases do not continue falling “at pace”.

“Decisions are going to have to be made on the basis of the evidence,” he told BBC news.

“If the evidence shows that the decrease in cases isn’t continuing, then clearly policymakers will have to consider much tougher measures.”

Mr Johnson said the case numbers remained “forbiddingly high” and that it would be a mistake to unlock in England if it were to lead to “another big rebound” in the disease.

On another bleak day, with a further 1,401 deaths across the UK of people who had tested for Covid-19 in the previous 28 days, there was some good news with evidence the various lockdown measures in place across the country were having an effect.

A sub-group of Sage said the reproduction number, the R, for coronavirus had fallen to below one across the UK, suggesting a retreating epidemic.

The Scientific Pandemic Influenza Group on Modelling (Spi-M) put the R, which represents how many people an infected person will pass the virus on to, at 0.8 to 1.0, down from 1.2 to 1.3 the previous week.

It said the number of new infections was shrinking by between 1% and 4% every day.

However Prof Whitty said the situation across the UK remained “extremely precarious”.

“A very small change and it could start taking off again from an extremely high base,” he said.

“If that happened again, we would be in really, really deep trouble.”

Professor Lawrence Young, a virologist at Warwick Medical School, suggested the more serious concern was the evidence that the South African and Brazilian variants may be less susceptible to the vaccines.

“The other virus variants identified in South Africa and Brazil are more worrying as they carry more changes in the spike protein of the virus,” he said.

“It is important that we now determine the neutralising ability of antibodies against virus variants generated in response to vaccination and study the immune response in individuals infected with virus variants.”

Sir Patrick said the evidence remained uncertain and there was no sign either the South African or Brazilian variants had any “transmission advantages” over those in the UK and so would not be expected to spread more quickly or “take over”.

But Public Health England medical director Dr Yvonne Doyle has said that it is still not “absolutely clear” the new variant coronavirus which emerged in the UK is more deadly than the original strain.

Boris Johnson announced on Friday that scientists had found the variant, which appeared late last year in south-east England, may be associated with “a higher degree of mortality”.

However Dr Doyle said more work was needed to determine whether that was actually the case.

“There are several investigations going on at the moment. It is not absolutely clear that that will be the case. It is too early to say,” she told the BBC Radio 4 Today programme.

“There is some evidence, but it is very early evidence. It is small numbers of cases and it is far too early to say this will actually happen.”