The UK was forced on Monday to confront that the South African variant of coronavirus was spreading within the country, as the health secretary pledged to “come down hard” on the strain.

The news came as the UK saw the number of people given their first jab of a Covid-19 vaccine rise to 9.3m with another 319, 038 first doses delivered. The government also hinted that it may share some of its vaccine supplies with other countries later in the year.

Speaking at a Downing Street press conference, Matt Hancock said the South African variant had been found in 11 people who had not travelled to the country where it was first detected. “There’s currently no evidence to suggest this variant is any more severe. But we need to come down on it hard, and we will,” he said.

Isolated cases of people infected with the variant, known as 501Y.V2, have been found in parts of London, the West Midlands, the East of England, the South East and the North West. “Surge testing” will be rolled out in all neighbourhoods where the new variant has been detected.

Everyone over the age of 16 living in the affected areas is being encouraged to get tested, whether or not they have symptoms, Mr Hancock added. “It is vital that we do all we can to stop transmission of this variant and I strongly urge everyone in these areas to get tested, whether you have symptoms or not,” he said.

There has been particular concern about the 501Y.V2 variant which has spread like wildfire across South Africa, because it has shown some signs of resistance to the current crop of vaccines. Moderna found that its vaccine produced six times lower antibody levels against the 501Y.V2 variant compared with other strains in circulation.

Like the B.1.1.7 variant that has come to dominate coronavirus infection across England, 501Y.V2 is more transmissible than older forms of the virus. Which of the two is more contagious is not known. But South African scientists studying 501Y.V2 have found no evidence that it results in worse outcomes.

But Susan Hopkins, senior medical adviser to Public Health England, said trials had suggested that the three vaccines approved in the UK remained effective against the new strain.

“We expect all other vaccines to have a similar level of effectiveness, particularly in reducing hospitalisation and death,” she said, adding it was likely that “a booster shot — a bit like the annual flu vaccine” would be required to improve immunity.

Mr Hancock also announced that an additional 40m doses of the Valneva vaccine had been ordered by the UK and it would potentially share vaccine supplies later this year once the most vulnerable had been jabbed.

“I want to say this to our international partners — of course I’m delighted how well this is going at home but I believe fundamentally the vaccine rollout is a global effort. We will protect UK supply and play our part to ensure the whole world can get the jab.”

Rooting out and preventing onwards transmission of each individual case of infection with this variant is seen as a crucial precautionary measure in case vaccines and therapeutic treatments continue to prove less effective, or it is determined that the strain leads to more severe outcomes.

“The discovery of a handful of cases with no links to travel to Africa, indicates that it might be more widespread in the community than previously thought,” said Simon Clarke, associate professor in cellular microbiology at the University of Reading.

A total of 105 cases of the 501Y.V2 variant have been found in the UK since December 22, most of which came from people who had recently travelled from South Africa.

The cases were identified by taking random samples of about 5-10 per cent of positive test results from around the country and sequencing the virus.

“As only 5 per cent of cases are tested to determine if they are the variant, there is a high probability that further local cases are in circulation,” said Rowland Kao, professor of veterinary epidemiology and data science at the University of Edinburgh, making it more difficult to contain its spread.

One senior government official said it was believed the 11 cases that did not directly originate from South Africa did nonetheless have some sort of “travel link”. “Clearly not a first-generation travel link, but second or third,” the official said.

“We’re trying to restrict the spread and get on top of this in a way we were not able to with the first variant,” the official added, saying that there was no evidence so far that the variant identified in South Africa was any more transmissible than the B.1.1.7 variant first identified in Kent and London.

In Surrey, where door-to-door testing started on Monday, the council said: “Residents in the affected areas . . . should remain calm and continue to follow the national restrictions that are currently in place.”

Meanwhile, prime minister Boris Johnson said he was “optimistic” that Britons would be able to have summer holidays. “I don’t want to give too much concrete by way of dates for our summer holidays. I am optimistic . . . but some things have got to go right,” he said during a visit to Yorkshire.