No 10 has defended its decision not to ban travel from India sooner, amid concern that the coronavirus variant first discovered there is now spreading quickly in parts of the UK.
India was reporting more than 100,000 cases a day by 5 April, but was not added to the red list until 23 April.
The government said the UK has “some of the toughest border measures”.
It comes after the British Medical Association raised concerns about Monday’s relaxation of Covid rules.
Prime Minister Boris Johnson said on Friday that the B.1.617.2 Indian variant could pose “serious disruption” to the final stage of lockdown easing in England on 21 June – but insisted Monday’s easing would go ahead as planned.
Scientists advising the government are confident the Indian variant spreads more easily, with cases of it nearly tripling to 1,313 in the past week in England.
Asked why the borders were not closed sooner, a government spokesman told the BBC: “We took precautionary action to ban travel from India on 23 April, six days before this variant was put under investigation and two weeks before it was labelled as of concern.
“Prior to India being placed on the red list in April anyone coming to the UK had to test negative and quarantine for 10 days.”
By the time the travel ban came into force, daily Covid cases in India had risen above 330,000.
Surge testing is now taking place in targeted areas across England where virus variants have been found, including postcodes within several London boroughs, Sefton, Worcestershire, and Nottingham.
Despite concern about the Indian variant, coronavirus restrictions across England, Scotland and Wales are due to be relaxed from Monday.
Which rules are easing varies across the devolved nations, but there will be a greater degree of indoor mixing allowed and more hospitality venues will be able to reopen.
Northern Ireland is due to review its restrictions later this month.
On Saturday, the British Medical Association said it had serious concerns about the decision to continue with the easing of lockdown restrictions.
“It is a real worry that when further measures lift on 17 May, the majority of younger people, who are often highly socially mobile and could therefore be most at risk of a more infectious strain, are not yet vaccinated,” said the BMA’s Dr Richard Jarvis.