A door-to-door testing blitz of 80,000 people in England is aiming to find "every single case" of the South Africa coronavirus variant in a bid to stop the spread of the more infectious strain.
Eleven cases of the variant identified over the past week were in people who had no links to travel, prompting concerns the mutation may be spreading in communities.
Mobile testing units and home testing kits will be deployed to areas where the variant has been discovered as the UK Government looks to prevent it getting a foothold.
Health Secretary Matt Hancock told a Downing Street press conference: "It's a big effort getting this new variant... essentially finding every single case of it, that is the goal."
Mr Hancock said the the door-to-door testing regime, along with enhanced contact tracing efforts, was an attempt to "come down on it hard".
It was "absolutely vital" that people minimise all social contact in the areas where South African cases had been identified, he added.
The eight postcode areas at the epicentre of the intensified testing programme, after 105 cases of the South Africa strain were identified in total, are: Hanwell, west London; Tottenham, north London; Mitcham, south London; Walsall in the West Midlands; Broxbourne, Hertfordshire; Maidstone, Kent; Woking, Surrey; and Southport, Merseyside.
Public Health England (PHE) is studying whether those who have already had the vaccine could need a booster shot "a bit like the annual flu vaccine" to help protect them against Covid-19 mutations, such as the South Africa, Brazil and Kent variants.
The South African variant is thought to be as transmissible as the variant that was first identified in Kent but there is no evidence yet that it causes more severe disease.
Dr Susan Hopkins from Public Health England (PHE) said three different vaccines trialled so far had shown effectiveness against the South African variant at a level higher than the minimum standard set by the World Health Organisation and the US Food and Drug Administration.
"We expect all other vaccines to have a similar level of effectiveness, particularly in reducing hospitalisation and death," she said, adding that laboratory studies were being carried out to provide further evidence.
The worry that the South Africa variant was spreading across England came as reports suggested scientists had recommended ministers should have gone harder with their border controls to stop new variants from entering the country.
The Scientific Advisory Group for Emergencies (Sage), according to The Times, said only mandatory hotel quarantines for all arrivals or a total border shutdown would keep mutations at bay.
A week after the advice was reportedly given to the UK Government, the Prime Minister outlined his plan for travellers coming from 30 "red list" countries to face up to 10 days in hotel self-isolation, with no date yet set for when the rules will start to be enforced – proposals lighter than those pushed by Sage.
Labour's shadow home secretary Nick Thomas-Symonds called for the Home Office to "reverse this reckless policy of leaving our borders unlocked and open to further risk".
He said: "Ministers have knowingly left the UK border open and potentially exposed people to new strains of the virus, in direct contradiction of their own Government scientists' advice.
"This puts the gains of the vaccine at risk, with disastrous consequences for people's lives.
"The Home Secretary needs to come to Parliament urgently and reverse this reckless policy of leaving our Borders unlocked and open to further risk."
In vaccine programme developments, Mr Hancock said almost nine in 10 of all those aged over 80 had been vaccinated, with over half of those in their 70s receiving a jab.
Data up to January 31 shows 9,296,367 first doses of the vaccine have been given, a rise of 319,038 in 24 hours.
The latest figures show that an average of 407,402 first doses of vaccine are needed each day in order to meet the Government's target of 15 million first doses by February 15.
Official figures showed a further 406 people had died within 28 days of testing positive for Covid-19 as of Monday, bringing the UK total to 106,564.
There had been a further 18,607 lab-confirmed cases of coronavirus in the UK – the lowest daily total of new cases since December 15.