Early evidence from Public Health England (PHE) published on Thursday suggests this version of Covid-19 may lead to an increased risk of being admitted to hospital compared with the previously dominant Kent variant (Alpha).
A mutated virus has been spotted in Nepal and elsewhere.
In England, the cases are spread across the country, and the most affected areas include Bolton in Greater Manchester (2,149 cases), Blackburn with Darwen in Lancashire (724), Bedford (608), Leicester (349), Manchester (278) and Birmingham (223).
Epidemiologist Professor Neil Ferguson, a member of the United Kingdom government's New and Emerging Respiratory Virus Threats Advisory Group, said the current "best estimate" was that the Delta variant could be "60% more transmissible" than the Alpha variant.
Lower neutralising antibody levels may still be associated with protection against Covid-19, the experts say. There are very little chances of us finding a variant unique to this region.
The group says cases of all COVID-19 variants went down from April to May, except for the Delta variant.
He told BBC Radio 4's Today programme that given the "more negative direction" of the data, a cautious approach is needed as the Government balances the potential risks against a desire for normality.
The number of deaths remained relatively low, however, with 11 more reported, reflecting the impact of a vaccination campaign that has delivered one dose to three-quarters of adults and two to just over half.
Professor Hunter says: "What we can be confident about with available data is that if you have had one or preferably two doses of vaccine you are rather less likely to catch either Alpha or Delta variants and even if you do become infected you are less likely to need hospital admission".
After a backlash from local health and council leaders who claimed they had not been alerted to the new advice, ministers have now backtracked and updated the guidance so that it asks people to minimise travel rather than avoid it altogether.
According to the Telegraph, a two-week delay to the final stage of Boris Johnson's road map will be used to accelerate second jabs for over-40s, moving from a 12 to eight-week gap between doses, echoing the practise that is already in place for over-50s. "This will reduce UK's rising risk from the Delta variant". Evolutionary pressure induced by largescale immunity might have forced the virus to undergo certain deletions in its spike protein for survival in hosts making them susceptible.
Most of these mutations are harmless but some can make the disease more infectious or threatening, and evade protection gained through infection or vaccination.
Current vaccines have been designed for earlier versions of coronavirus, but scientists believe they should still work, although they may be less effective.
He said that this dual threat - that the new mutation could make the virus more transmissible and more resistant to vaccines - means scientists are monitoring it carefully.
Facebook suspension of Trump to last 2 years
Trump has received the maximum penalty under those rules, "given the gravity of the circumstances" leading to his suspension. Facebook has revisited Donald Trump's "indefinite" suspension following a recommendation from the Oversight Board.