Surge testing is being introduced to parts of west London after cases of the Indian coronavirus variant were detected.
People living and working in specific areas of Harrow, Ealing, Hillingdon and Brent will be advised to take a PCR test even if they do not have symptoms.
Local authorities will “shortly confirm” the areas where additional testing will be offered within those boroughs, the Department of Health and Social Care (DHSC) said.
NHS Test and Trace is providing testing and genomic sequencing in education settings and targeted areas across the four boroughs, following the identification of the B1617.2 strain.
Those who tested positive for the variant have been told to self-isolate and their contacts are being identified.
People who have symptoms can book free tests online or by phone, while those without symptoms are advised to visit their local council’s website for more information.
Along with increased testing in the boroughs, so-called “enhanced contact tracing” – whereby tracers look back over an extended period of time to determine the route of transmission – will be used for those who test positive with a variant of concern.
Mayor of London Sadiq Khan said: “I urge everyone who lives, studies or works in these five boroughs to visit the website of their local authority for more details and to take a test as soon as they are offered it.
“It’s vital that everyone also accepts the vaccine as soon as possible and I continue to urge the Government to increase the availability of the vaccine to younger age groups who live where this variant is spreading.”
Cases of the Indian variant of coronavirus in the UK have risen by more than 2,000 in the space of a week, according to figures from Public Health England (PHE).
The latest weekly data showed there were 3,424 cases of the B1617.2 mutation – an increase of 2,111 on the previous week.
While most cases were concentrated in the North West – particularly Bolton – and London, PHE said it was seeing “clusters of cases” across the country.
Dr Meera Chand, the Covid-19 incident director at PHE, said it was essential people in the worst-affected areas who had yet to receive their second dose of the vaccine came forward as soon as it was offered.
“This is vitally important in the light of our current assessment that (B1617.2) has grown rapidly in England and may be highly transmissible,” she said.