Health Secretary Matt Hancock announced at the Downing Street briefing on Wednesday evening that the testing – and an increase in vaccinations – was being introduced in Hounslow as well as Bedford, Burnley, Leicester, Kirklees and North Tyneside.
Figures today revealed that the number of cases of the variant, known as B1.617.2, have increased in the capital from 400 to 720.
On Thursday, Public Health England put Hounslow in sixth place on its national covid “watch list”.
Mayor Sadiq Khan told the Standard today that additional surge testing was due to be deployed across all five boroughs.
He said: “There are north-west [London] boroughs where there appears to be high numbers of people with the variant first discovered in India.
“Hounslow, the Government already announced, has got additional support – mass surge testing is taking place.
“The other boroughs where there are larger numbers of this strain are Hillingdon, Harrow, Brent and Ealing.
“Those boroughs are working incredibly closely together. There is additional mass surge testing taking place there, which means additional PCR tests.
“There is also genomic sequencing taking place across London to see how many people have tested positive for this particular strain.”
Mr Khan said there was also additional support for people self-isolating and for contact tracing. “We are keen to make sure that this virus doesn’t spread faster than would otherwise be the case, and we are working on a pan-London basis.”
It is understood that while there is concern at the increasing number of cases of the variant in London, there is not a worry that the spread is getting out of control.
About a quarter of the first 400 cases in the capital were linked to international travel, with the majority of the remainder being family members or close contacts.
In Hounslow, checks are being done on “quarantine hotels” to establish if people harbouring the virus have passed it to hotel staff and then on into the community. Concerns about these hotels were raised in Parliament earlier this week by Brentford and Isleworth MP Ruth Cadbury.
Vaccination staff in the five boroughs are said to be taking a pro-active approach to offering jabs to younger Londoners who may not be entitled to receive a vaccine on the basis of their age.
This is to limit the spread of infection in multi-generational households that are common across Asian communities in west London, and to avoid turning away people who may otherwise be hard to reach.
Public Health England also revealed on Thursday night that the number of cases of the Indian variant across the country had increased by 2,111 in a week to 3,424.