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The coronavirus Delta variant is now in every council in England apart from one, official data from Public Health England shows.

The Covid-19 strain, which was first identified in India, has contributed to an increase in the number of new infections.

The total number of cases attributed to the mutation now stands at 42,323 and the strain is understood to account for more than 90 per cent of new Covid infections across the country.

PHE estimates the strain is 60 per cent more transmissible compared with the previously dominant Alpha, or Kent, variant, and that cases are doubling every four-and-a-half days in some parts of England.

Blackburn has recorded a high number of Delta variant cases
(Image: Julian Hamilton/Daily Mirror)

The only area in England that has not recorded any case of the Delta variant is the Isles of Scilly off the coast of Cornwall, PHE told Mail Online.

Bolton has been the worst affected area in the country with 3,896 cases.

In Blackburn with Darwen there are 1,924 Delta variant cases, in Manchester 1,580 and in Birmingham 1,076.

Meanwhile, Merton Council in south London has announced that it is stepping up surge testing in two areas – including an industrial estate in New Malden – where there have been recent outbreaks.

Shoppers on Oxford Street in central London following the further easing of lockdown restrictions in England
(Image: PA)

Additional testing is also being carried out in Staffordshire and in Northwich and Winsford in Cheshire.

A scientist advising the Government has said the emergence of the variant means ministers should be cautious about lifting lockdown measures.

Professor Peter Openshaw, a member of the Nervtag advisory group, told the BBC Radio 4 Today programme: "It is such a disappointing setback that there is another variant that seems even more successful than the previous variants.

"This Delta variant seems to be about 60 per cent more transmissible than that (the Alpha variant).

"So it really has gone up another gear and that means that we really have to double down and not lose all the advantage that has been gained by the massive effort that has been put in so far."

But a potential delay of lifting all lockdown measures – reportedly from June 21 to July 19 – will come as a bitter blow to many businesses, particularly in the hospitality and leisure sectors.

Today, Boris Johnson cast fresh doubt on the potential lifting of lockdown restrictions after admitting data he was seeing were “worrying”.

Boris Johnson said the latest Covid data were 'worrying'
(Image: Sky News)

The Prime Minister said evidence coming in was a “ serious, serious concern ” as he prepares to announce on Monday whether Freedom Day is being delayed.

He is said to be considering whether to order a two-week or four-week postponement to the relaxation of curbs that was pencilled in for June 21.

He told Sky News: "It's clear that the Indian variant is more transmissible and it's also true that the cases are going up, and that the levels of hospitalisation are going up.

“We don't know exactly to what extent that is going to feed through into extra mortality, but clearly it's a matter of serious, serious concern."

The PM added: “What we want to do is make sure that the roadmap is irreversible, but you can't have an irreversible roadmap unless you're prepared to be cautious.

“Some of the data is still open to question, but we'll be making an announcement on Monday."