The variant of Covid-19 first identified in India is now the dominant strain of the virus in England, data shows.
Figures published by Public Health England on Thursday show that the Delta variant has accounted for over nine in ten cases in the past two weeks.
The data comes as the Prime Minister considers whether to press ahead with the final stage of lifting lockdown restrictions on June 21, amid concern that Delta could lead to a significant rise in infections and hospital admissions.
Areas where Delta has the strongest foothold have already seen increases in both, as scientists fear that the strain is more transmissible than the previously dominant Kent variant, which emerged in the UK at the end of last year.
However, ministers have stressed that the evidence so far shows that the vaccine is very effective against the Delta variant and are continuing to urge people to get their jab.
Where is the Indian variant in the UK?
Data shows prevalence of the Indian variant continues to be highest in the North West of England in Bolton and Blackburn with Darwen – two local authorities that have seen extra vaccinations deployed in an attempt to protect residents against Delta’s tightening grip on their local areas.
Lab results in the two weeks up to May 22 suggested that more than 90 per cent of cases from the community in these areas were identified as Delta – up from 28.6 per cent in the two weeks to April 24 in Bolton and 18 per cent in Blackburn with Darwen.
The areas where the Indian variant is increasingly prevalent
In total Bolton has seen 2,060 confirmed cases of the Indian variant, while Blackburn with Darwen has seen 672.
Yet data suggests the variant has now spread beyond these hot spots to most of England now, with Croydon, Central Bedfordshire, Canterbury, Hillingdon and Reading among the local authorities seeing B.1.617.2 dominating local sequencing data in the two weeks to May 22.
Public health officials across the country are continuing to monitor the prevalence and impact of Delta, which the Prime Minister has previously warned could delay the final lifting of lockdown in England on June 21.
The Government is waiting for enough data to confirm to what extent Delta can spread more easily than previous strains of Covid-19, and potentially lead to a rise in severe cases of coronavirus among groups yet to get the vaccine.