UK cases of the Delta variant have risen almost four-fold in less than a month, with one expert saying the country is “firmly” in its third wave of Covid-19.

Public Health England figures show a total of 161,981 confirmed and probable cases of Delta variant have now been identified in the UK – up by 50,824, or 46%, on the previous week.

Of the 161,981 cases, 148,538 have been in England, 10,185 in Scotland, 1,749 in Wales and 1,509 in Northern Ireland.

The Delta variant, which was first identified in India, continues to account for approximately 95% of confirmed cases of coronavirus across the UK.

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On June 9, there were 42,323 confirmed and probable cases. The latest figure of 161,981, as of June 30, is nearly four times as high.

Professor Lawrence Young, a virologist from the University of Warwick, said: “This data is important to consider in the decision to open up on the 19th July.

“We may have weakened the link between infections, hospitalisations and deaths but this significant increase in infections with the Delta variant raises serious concerns.

“As the virus continues to spread in those who are unvaccinated or have only received one jab, it will result in more disease, including increasing the burden of long Covid.

“We are already seeing some of those who have been fully vaccinated getting infected and some of those become sick.

“And there is another worry – that as the virus spreads it will continue to generate new variants, increasing the risk that one will pop up that is more vaccine-resistant.”

Dr Jenny Harries, chief executive of the UK Health Security Agency, said: “Cases across the UK continue to rise and it is incredibly important that we do not forget to be careful.

“The best thing we can do to protect ourselves and the people we love is to get the vaccine if eligible, get tested twice a week and practise ‘hands, face, space, fresh air’ at all times.

“Although cases are rising, we are not seeing a proportional rise in the number of people who are being admitted to hospital.

“The data suggest this is testament to the success of the vaccination programme so far and clearly demonstrates the importance of getting both doses of the vaccine.”

It comes as new Office for National Statistics (ONS) data shows a rise in the number of people in England with Covid-19.

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Around one in 260 people in private households in England had Covid in the week to June 26 – up from one in 440 in the previous week.

This is the highest level since the week to February 27.

In Scotland, around one in 150 people are estimated to have had Covid-19 in the week to June 26 – up from one in 220 in the previous week.

For Wales, the latest estimate is one in 450 people, up from one in 830; and one in 670 people in Northern Ireland, compared with one in 720 in the previous week.

Professor James Naismith, director of the Rosalind Franklin Institute at the University of Oxford, said he thought the data was “unsettling”, adding: “We are firmly now in a third wave of cases.”

He said delaying the easing of restrictions had paid off by slowing things down, but he added: “The Delta variant is still growing despite track and trace, despite testing, despite restriction and despite masking.

“The Government commitment to release restrictions on July 19th means the rate of growth of infections will accelerate.

“It seems now unavoidable that Delta will sweep through the unvaccinated (mainly young).

“Although young people are at much less risk, it’s not zero. A wave on the scale of what now seems likely will result in lives being blighted”.

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He urged people to get vaccinated and suggested that those “who have had very weak immune responses to the vaccine” should shield.

He continued: “Increasing vaccination and time will end the Delta wave in the UK.

“Since track and trace has failed to hold back Delta (or before that Alpha) in Scotland and in the UK, it is unclear whether its retention has any value to public health, particularly given current vaccination rates.”

The professor also predicted a “rough” summer for Europe as Delta sweeps through countries there “in much the same way as here”.

Elsewhere, Dr Mike Tildesley, a member of the Scientific Pandemic Influenza Modelling group, which provides modelling evidence to the Scientific Advisory Group for Emergencies (Sage), told Times Radio the UK was not “quite there in terms of a peak” of a third wave.

He said experts had not yet seen a big rise in hospital admissions and deaths, “which is really strong evidence that actually the vaccines are working really, really effectively, helping to break that link between cases and hospital admissions.”

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Asked if vaccine efficacy was better than his team predicted in modelling for Sage, he said: “Oh to be honest that’s absolutely true.”

He said there is “always uncertainty – we have to try our best to capture that, but of course as we get more data, the uncertainty in our model predictions reduces.”

Regarding July 19, he said: “I’m cautiously optimistic that the 19th of July is looking certainly hopeful.”

But he said the country needed to get into the “mindset” of living with Covid-19.

On the risks around international travel, he added: “It’s a really difficult one because I mean, we’re doing very well domestically and in that sense, we’re in a really good position to get back to domestic freedom very soon.

“International travel is much more challenging but it is also something the Government needs to look at because clearly we know the travel industry have had a really, really tough year and a half now, and so they do need to look at trying to open up where it is safe to do so.

“I think travel within Europe is hopefully possible at some point over the summer but it’s going to have to be looked at on a case-by-case basis.”