The South African Covid variant has been discovered in south London, prompting surge testing in the area in a bid to stop the spread.
West Norwood and a small section of Streatham in the borough of Lambeth are the latest areas identified for a testing blitz.
They join areas of north London, West Midlands, Bristol and large parts of Manchester.
Door-to-door and mobile testing began at the start of the month after 11 cases of the variant were identified in people who had no links to travel – suggesting it may be spreading in communities.
Latest figures show 170 cases of the South African variant have now been identified in the UK.
Check if your postcode is in one of the targeted areas:
East of England (EN10)
London (W7, N17, CR4) and added on Tuesday: SE27 0, SE27 9 and SW16 2
North West (PR9)
West Midlands (WS2)
Areas in South Gloucestershire
Manchester (M14 4, M14 7, M15 5, M15 6, M16 7, M16 8)
Meanwhile the surge testing carried out in Woking, Surrey, which started last week, is now complete.
People living in the selected postcode areas are being strongly encouraged to take a Covid-19 test this week, whether they are showing symptoms or not.
When the targeted testing was first introduced, health secretary Matt Hancock warned the tens of thousands of people effected to take "extra special precaution" in order to avoid spreading the variant.
After being added to the list, Lambeth council said: “This is to help us track any potential cases after a case of the variant of Covid-19 that was first identified in South Africa was discovered in the area.”
People with symptoms should book a test in the usual way while others should visit their council website.
Dr Susan Hopkins, from Public Health England, told a briefing for journalists on Tuesday that 170 cases of the South African variant had been identified so far, including 18 that are not linked to travel.
It comes as Home Secretary Priti Patel is looking into the case of a passenger arriving in the UK from South Africa without receiving any checks.
On Monday, the deputy chief medical officer for England said it's unlikely the South African variant will become dominant in the coming months, unlike the strain which emerged last year in Kent which is now more dominant.
Professor Jonathan Van-Tam said: “We have small numbers of the South African variant in the UK at the present time.
“And as I’ve said, I’m not seeing, and the early modelling data do not suggest, a transmissibility advantage for this virus.
“It’s not going to kind of overrun or overtake the current B1.1.7 (Kent variant) virus in the next few months, or that is the most likely scenario, that it won’t happen.
“I don’t think that this is something that we should be concerned about right at this point in time."