Surge testing operations have been widened across London after further cases of the South African coronavirus variant were found.
Three boroughs in south London have set up additional testing facilities to process thousands of residents, while a case of the variant was also detected in Barnet, north London.
The Department of Health and Social Care (DHSC) confirmed the case in Barnet was unrelated to other clusters, but it had been isolated and the person’s contacts traced.
More than half a million adults living in south London boroughs have been offered tests, including 264,000 in Lambeth, 265,000 in Wandsworth, and 14,800 in the Rotherhithe ward of Southwark.
Some 44 confirmed cases of the variant have been found in Lambeth and Wandsworth, with a further 30 probable cases, the DHSC said.
Thousands of people queued up at pop-up testing facilities offering polymerase chain reaction (PCR) tests on Tuesday and Wednesday, and marshals said they had warned that waiting times could be up to two hours.
People aged 11 and over who live, work or travel through those areas are being urged to take a PCR test, on top of twice-weekly rapid testing.
Facilities set up in Wandsworth include centres at Wandsworth Town Hall, Tooting Leisure Centre and Mount Clare House, Roehampton, with more opening in Putney on Thursday.
Pop-up centres in Lambeth included Clapham Common, Brockwell Park, and Lambeth Town Hall.
Home-testing kits are available for collection by residents at multiple sites.
Additional testing has been set up by NHS Test and Trace in the SE16 area of Southwark, after a case was linked to the cluster in Wandsworth and Lambeth.
The DHSC said the person had been identified and was self-isolating, and their contacts had been traced.
Barnet Council said although the single case of the variant had been traced, residents in Finchley N3 were “strongly encouraged” to take a PCR test, even if asymptomatic.
“This week, a team working on behalf of Barnet Council will be going door to door to affected households in N3 to offer PCR home testing kits,” it said in a statement.
“Other people in affected areas will receive a leaflet asking them to get tested at a mobile testing unit (MTU) located in Finchley Central Underground Station car park.
“Regular shoppers in Ballards Lane are also encouraged to get tested at the MTU.”
Downing Street has insisted the outbreak is being taken “very seriously” and “strong measures” have been put in place to prevent it spreading.
A DHSC spokesperson said: “Additional surge testing and sequencing has been successfully rolled out in a number of targeted locations to help us suppress, control and better understand Covid-19 variants in circulation.
“Surge testing has been well received by the public in those areas, with thousands of tests completed and thousands of genomes sequenced.”
The BBC reported that the outbreak appears to have been triggered by an individual who travelled from Africa in February.
According to documents seen by the broadcaster, the country involved was not on the red list for mandatory hotel quarantine at that time, but is now.