ITV News Science Editor Tom Clarke explains how significant the development is.
The biggest Covid surge testing operation to date is beginning across a huge area of south London, amid concerns about a "significant" number of South African variant cases.
A testing blitz is being carried out across Wandsworth and Lambeth, where 44 confirmed cases, and 30 probable cases, of the variant first identified in South Africa have been found.
The variant is deemed to be more transmissible than the UK one, which was already classed as being more prolific than the original coronavirus.
How worried should we be about surge testing in South London? Science Editor Tom Clarke explains
It comes as England's lockdown eased further on Monday - with pub gardens reopening and non-essential shops welcoming customers once more.
Health authorities stressed all identified have been told to self isolate and their contacts are being tested, but admitted the "cluster" was "significant".
Dr Susan Hopkins, Chief Medical Adviser for NHS Test and Trace said: "The cluster of cases of the variant first identified in South Africa found in parts of South London, predominantly the Lambeth and Wandsworth areas is significant.
"It’s really important people in the local area play their part in stopping any further spread within the local community."
The population of the two boroughs, around 650,000 in total, is being encouraged to get tested for the virus - with everybody over the age of 11 asked to come forward.
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The first case of the variant in the area was identified in early March.
Health authorities said it was the largest surge testing operation to date. Similar programmes have taken place in Gloucestershire, Ealing and Redbridge among other places.