UK Health Minister Matt Hancock has said there is "high degree of confidence" that current vaccines are effective against the UK Covid variant.
He also said that there were early signs that the lockdown was working, an assertion seemingly corroborated by the daily case rate figures which on Monday were at their lowest since the beginning of the year.
The UK reported 22,195 new confirmed infections, well down from Sunday's figure of 30,004.
Deaths were also marginally lower, at 592 compared to yesterday's 610.
In further good news Mr Hancock revealed that four in five over 80s had now received their first vaccine dose and that the proportion of people refusing to be inoculated was very low.
He did caution that vaccine supplies were getting "tight" but will have been reassured by the findings of a leading British immunologist who said on Monday that “rock solid” evidence proves there is no need to reduce the gap between doses from the current 12-week period.
Professor Adam Finn from the University of Bristol rebuked the British Medical Association after the doctors' association called for a shorter gap between Pfizer/BioNTech vaccine doses in the UK.
The remarks came as Prof John Bell, a UK government scientific adviser, said Covid-19 was becoming "more efficient at living in humans", as he highlighted the complexity of new strains of the virus found in South Africa and Brazil.
Prime Minister Boris Johnson said the "vaccine-busting" new variants of coronavirus had forced him to consider toughening the UK's border controls with the cabinet to decide on Tuesday whether to introduce hotel quarantine for new arrivals.
"We have to realise there is at least the theoretical risk of a new variant that is a vaccine-busting variant coming in - we've got to be able to keep that under control," he said.
"We want to make sure that we protect our population, protect this country against reinfection from abroad."
Mr Johnson confirmed that the was looking at the option of quarantine hotels - where inbound travellers pay to be isolated at a hotel on arrival. In Australia, arrivals have to quarantine for a minimum of 14 days at a hotel.
"That idea of looking at hotels is certainly one thing that we are actively now working on," he said.
The UK last week closed all of its remaining travel corridors, forcing all new arrivals to enter mandatory 10-day quarantine at home, as Mr Johnson said the country needed to guard the inoculation programme from new variants of the virus.
More than 6.3 million people in the UK have been given their first dose of the Covid-19 vaccine, including three-quarters of those aged over 80.
But the BMA on Sunday warned that the current 12-week gap between the first and second doses could reduce the effectiveness of the shot.
Pfizer recommends 21 days between doses but the UK medicine regulator allowed the longer window to give more people at least some level of protection against the virus.
BMA chairman Dr Chaand Nagpaul said the UK should follow “best practice” and reduce the gap to six weeks.
He pointed to World Health Organisation analysis that said second doses of the Pfizer/BioNTech vaccine should only be delayed “in exceptional circumstances”.
Prof Finn, however, said there was a strong body of evidence from other vaccines, including the Oxford/AstraZeneca product, that shows levels of protection do not diminish over 12 weeks.
"It's likely there will be persistent and even increasing protection over that time," he told the BBC's Radio 4 Today programme. "We know that for the Oxford vaccine and we know it for many other vaccines as well."
He criticised the BMA for failing to “understand the issues” before making a public statement.
“This ‘absence of evidence’ story ignores the fact that there is rock solid evidence that if you give the dose to more people you give them protection and save lives,” Prof Finn said.
Pfizer and BioNTech said earlier this month there was “no data” to support the change in vaccination schedule, warning that its dose was not designed for the longer window.
Researchers at the University of Bristol are currently analysing hospital data to determine if the extended time between vaccines was having an effect on admission rates among people inoculated.
Prof Finn said the results of this study will be released within two weeks.
Meanwhile, Mr Johnson said the government would be "looking at the potential of relaxing some measures" before mid-February.
MPs had been calling for Number 10 to lay out a "route map" for reopening schools after Health Secretary Matt Hancock suggested at the weekend they may remain closed until Easter.
A dozen Conservative Party MPs warned publicly that pupils risk becoming the pandemic's "forgotten victims" and demanded schools fully reopen sooner.
The group - which includes former Cabinet minister Esther McVey and Graham Brady, head of an influential committee of Conservative backbenchers - backed a parents' pressure group campaign on the issue.
"We need to get our children learning again," Conservative MP for Harlow Rob Halfon, chairman of parliament's watchdog education committee, said on Twitter.
"The engine of government should be directed towards opening our schools. We face an epidemic of educational poverty and mental health otherwise."
Mr Johnson said the government would tell teachers and parents when schools in England could reopen "as soon as we can".
"We've now got the R [reproduction rate] down below 1 across the whole of the country, that's a great achievement, we don't want to see a huge surge of infection just when we've got the vaccination programme going so well and people working so hard," he said.
"I understand why people want to get a timetable from me today, what I can tell you is we'll tell you, tell parents, tell teachers as much as we can as soon as we can."
