The UK has identified 77 cases of the coronavirus variant first detected in South Africa, the health secretary has said.
Cases are linked to travellers arriving in the UK, rather than community transmission, Matt Hancock added.
He told the BBC’s Andrew Marr cases were under “very close” observation and enhanced contact tracing was under way.
Ministers are due to meet on Monday to consider imposing tougher restrictions on people arriving from abroad.
Scientists have said there is
Meanwhile, Mr Hancock said 75% of over-80s and three quarters of care homes in the UK have received a first Covid jab.
Both the Pfizer-BioNTech and Oxford-AstraZeneca vaccines require two doses, and figures so far reflect those given the first dose.
All viruses, including the one that causes Covid-19, mutate, and variants have been first located in the UK, South Africa and Brazil.
The South Africa variant has been found in at least 20 other countries, including the UK.
Mr Hancock said that all the South Africa variant cases in the UK were linked to travel.
“That’s why we have got such stringent border measures in place against movement from South Africa,” he added.
The UK closed all travel corridors last week until at least 15 February, with almost all travellers arriving in the country now required to show proof of a negative Covid-19 test to be allowed entry.
Prime Minister Boris Johnson has not ruled out bringing in tougher measures at UK borders, telling a Downing Street news conference on Friday: “We don’t want to put that (efforts to control Covid) at risk by having a new variant come back in.”
Ministers are set to discuss whether to tighten border restrictions further, including the possibility of hotel quarantines for travellers.
Mr Hancock said: “We have got to be cautious at the borders.”
Government data on 14 January showed there were 35 confirmed cases of the South Africa variant identified in the UK, and a further 12 “probable” cases.
Mr Hancock said nine cases of the Brazil variant had been found in the UK, adding “we are monitoring each and every one very closely”.
Shadow foreign secretary Lisa Nandy told the BBC’s Andrew Marr Show that Labour had been “pushing the government to take tougher measures at the border since last spring”.
She said: “We would fully expect the government to bring in tougher quarantine measures, we would expect them to roll out a proper testing strategy and we would expect them as well to start checking up on the people who are quarantining.
“Only three out of every hundred people who are asked to quarantine when they arrive into the UK actually face any checks at all – that’s just simply not sufficient.”
On Friday, Mr Johnson said there was “some evidence” the UK variant may be associated with “a higher degree of mortality”.
The UK government’s chief scientific officer, Sir Patrick Vallance, said there was “a lot of uncertainty around these numbers” but that early evidence suggested the variant could be about 30% more deadly.
The PM said on Friday that there was evidence that both the Pfizer-BioNtech vaccine and Oxford-AstraZeneca jab were effective against the variant first detected in the UK.
Sir Patrick has warned that the variants in South Africa and Brazil might “have certain features which means they might be less susceptible to vaccines”.
But he said “there is no evidence” that the two variants have transmission advantages over those already in the UK and so having cases here doesn’t mean “they will take off”.
Meanwhile, England’s deputy chief medical officer warned that people who have received a Covid-19 vaccine could still pass the virus on to others and should continue following lockdown rules.
Writing in the Sunday Telegraph, Prof Jonathan Van-Tam stressed that scientists “do not yet know the impact of the vaccine on transmission”.
He said vaccines offer “hope” but infection rates must come down quickly.
Can vaccinated people spread coronavirus?
It’s a key question but the fact is that no one can be sure.
That’s because the trials of the vaccines explored the safety of the drugs and how well they prevent people from becoming ill – with good results for both.
But they did not investigate whether vaccination also stops infection and therefore whether people who’ve been immunised can still spread the virus to others.
If a vaccinated person did become infected, they probably wouldn’t realise because they wouldn’t have any symptoms. That’s why health officials and ministers are so concerned.
It’s possible that the antibodies boosted by the vaccine suppress the effects of the virus but don’t eliminate it from the upper airway.
Many scientists are cautiously hopeful that in this scenario, the amount of virus would be reduced but they’re waiting for the results of studies under way now.
And until there’s an answer, it’s difficult to calculate how and when it’s safe to ease restrictions and allow people to mix again.
Another 1,348 deaths within 28 days of a positive coronavirus test were reported in the UK on Saturday, in addition to 33,552 new infections.
There were 4,076 Covid patients on mechanical ventilators in UK hospitals as of Friday, according to government data.
That is higher than during the first wave, when the peak was 3,301 on 12 April.
In other developments:
- Israel’s health minister Yuli Edelstein said some people “still get sick” with coronavirus after getting the first dose of the vaccine, but that there are “some encouraging signs of less severe diseases, less people hospitalised after the first dose”.
- Ministers have been urged to intervene after 500 staff at the UK vehicle licensing agency’s contact centre in Swansea contracted coronavirus.
- Fines amounting to more than £15,000 have been issued after 300 attended a rave in Hackney, and a student party in Birmingham broken up by police attracted people from up to 200 miles away.