Larges queues have formed in south London as hundreds of thousands more are being urged to get tested to try and stamp out a "concerning" strain of the virus which causes Covid-19.

One expert said "none" of the vaccines are as effective against the South African variant - though studies suggest that the jabs still prevent severe disease and death.

Rapid surge testing has been deployed in four London boroughs - with all adults in Wandsworth and Lambeth being asked to get a test and people in specific areas of Barnet and Southwark also invited to perform at test.

Coronavirus surge testing in Brockwell Park, south London. Michael Bedigan/PA Wire

Coronavirus surge testing in Brockwell Park, south London. Michael Bedigan/PA Wire

The Prime Minister's official spokesman said Boris Johnson took the situation "very seriously" and recommended for everyone to "take up that invitation" to get tested.

Large queues have been forming outside test centres in these south London boroughs.

People take part in coronavirus surge testing on Clapham Common, south London. Michael Bedigan/PA Wire

People take part in coronavirus surge testing on Clapham Common, south London. Michael Bedigan/PA Wire

Coronavirus surge testing on Clapham Common, south London. Michael Bedigan/PA Wire

Coronavirus surge testing on Clapham Common, south London. Michael Bedigan/PA Wire

Meanwhile, the Government is considering making vaccination of people working in care homes with older adults mandatory.

Concerns have been raised about the low take-up of the vaccine in many care homes.

The Department of Health and Social Care launched a consultation on making Covid-19 vaccination a "condition of deployment" for care home staff.

People take part in coronavirus surge testing on Clapham Common, south London. Kirsty OConnor/PA Wire

People take part in coronavirus surge testing on Clapham Common, south London. Kirsty O'Connor/PA Wire

Commenting on surge testing, Professor Anthony Harnden, deputy chairman of the Joint Committee on Vaccination and Immunisation (JCVI), told Good Morning Britain: "From a vaccine point of view the South African variant is of concern.

"We know from studies that none of the vaccines are as effective against the South African variant - though the vaccines still prevent against severe disease and death even with the South African variant.

"The problem is, they may not protect against infection which allows infection to transmit, and if we allow transmission through the community in large numbers with high infection rates then we could see other variants emerging."

Data up to April 7 suggests there have been 544 cases of the South African variant found in the UK in total, including 533 gnomically confirmed cases and 11 probable cases.

People take part in coronavirus surge testing on Clapham Common, south London. Kirsty OConnor/PA Wire

People take part in coronavirus surge testing on Clapham Common, south London. Kirsty O'Connor/PA Wire

Surge testing involves swabbing people without any symptoms of the virus to see if they are infected using tests which are assessed in a laboratory setting - also known as a PCR test. These are different to the 30 minute lateral flow tests.

Coronavirus surge testing on Clapham Common, south London. Michael Bedigan/PA Wire

Coronavirus surge testing on Clapham Common, south London. Michael Bedigan/PA Wire

Population data show that more than half a million adults live in the areas being asked to take tests as part of the surge testing programme.

Health officials said that the surge testing in Finchley, Barnet, was launched after a single case of the South African variant was identified.

The Department of Health and Social Care said that genomic sequencing indicates that the case is "not linked" to the cluster identified in South London.

Coronavirus surge testing on Clapham Common, south London. Michael Bedigan/PA Wire

Coronavirus surge testing on Clapham Common, south London. Michael Bedigan/PA Wire

In other developments, a "mix and match" trial assessing the use of two different types of Covid-19 vaccines in the same person was extended.

So far, the UK has passed 40 million doses, of which eight million are second doses, and the Office for National Statistics suggest that across the UK, half the adult population would test positive to Covid-19 antibodies.

Prof Harnden has urged people "not to go wild" and said people should not behave in the same way as they did before the pandemic.

Mr Johnson said on Tuesday that although vaccines had helped, lockdown restrictions had done "the bulk of the work" in reducing Covid-19 infections.

And he warned that the easing of lockdown restrictions will "inevitably" lead to more infections and deaths.

Asked about the remarks, Prof Harnden told BBC Breakfast: "I think he's probably concerned, as I am, about the scenes in London that we saw of people actually enjoying the outside, pubs and then the crowded spaces - well, of course what that will do is push infection rates up.

"And new variant strains such as the South African strain - we really don't want that to become prevalent in this country because of course the vaccines don't work quite as well (against it).

"We will all want to get our lives back, we all want to enjoy ourselves again, but we must be cautious and do this slowly. Otherwise we'll get back to square one."

But the Prime Minister's spokesman said there is "nothing to suggest" that the vast majority of the public "aren't behaving responsibly" since the lockdown was eased this week.