There has been a 79% rise in one week in cases of the Delta variant first identified in India, Public Health England (PHE) has said.
Dr Jenny Harries, chief executive of the UK Health Security Agency, said the increase across the UK is being driven by younger age groups, many of whom have now been invited for a vaccination as the jab rollout extends to anyone aged 18 and over.
Hospital cases have also almost doubled, though most of those needing treatment have not had a vaccine.
It came as the Prime Minister said he is “very confident” that the remaining coronavirus restrictions in England will be lifted on July 19.
Speaking at Kirklees College in Dewsbury, West Yorkshire, Boris Johnson said: “I’m very confident that we’ll be able to go through with step four of the road map on the timetable that I’ve set out with treating July 19, as I’ve said, as a terminus date. I think that’s certainly what the data continues to indicate.”
The PHE data shows that 75,953 confirmed and probable cases of the Covid-19 Delta variant have now been found in the UK – up by 33,630, or 79%, on the previous week.
Of the 75,953, some 70,856 have been in England, 4,659 in Scotland, 254 in Northern Ireland and 184 in Wales.
The most recent data shows 99% of confirmed and probable cases of coronavirus across the country are the Delta variant.
Dr Harries said: “Cases are rising rapidly across the country and the Delta variant is now dominant.
“The increase is primarily in younger age groups, a large proportion of which were unvaccinated but are now being invited to receive the vaccine.”
The latest Office for National Statistics (ONS) figures show that around one in 520 people in private households in England had Covid-19 in the week to June 12.
This is up from one in 560 in the previous week and the highest level since the week to April 10.
Meanwhile, 806 people in England have been admitted to hospital with the Delta variant of Covid-19 as of June 14, a rise of 423 on the previous week, according to PHE data.
Of the 806 admitted, 527 (65%) were unvaccinated, 135 (17%) were more than 21 days after their first dose of vaccine, and 84 (10%) were more than 14 days after their second dose.
As of June 14, there have been 73 deaths in England of people who were confirmed as having the Delta variant and who died within 28 days of a positive test.
Of this number, 34 (47%) were unvaccinated, 10 (14%) were more than 21 days after their first dose of vaccine and 26 (36%) were more than 14 days after their second dose.
Dr Harries said: “It is encouraging to see that hospitalisations and deaths are not rising at the same rate, but we will continue to monitor it closely.
“The vaccination programme and the care that we are all taking to follow the guidance are continuing to save lives.
“Please make sure that you come forward to receive both doses of the vaccine as soon as you are eligible. Don’t drop your guard – practice hands, face, space, fresh air at all times.”
New documents released on Friday by the Scientific Advisory Group for Emergencies (Sage), which advises the Government, show that around 65% of people admitted to hospital with Covid-19 were discharged.
A paper compiled on June 9, which included 884 patients included in the analysis, shows that between May 1 and June 1, 52 died and 89 required treatment in an intensive care unit, while 577 were discharged home.
There were more male (52%) Covid-19 patients in the hospital than females (48%), with deaths mostly occurring amongst over 70s.
Of those admitted, 784 patients required some form of oxygen treatment.
Elsewhere, the latest figures from NHS England show that an estimated four in five adults in England have received their first dose of Covid-19 vaccine.
The data shows that 35,507,916 first doses have been delivered up to June 17, the equivalent of 80.2% of all people aged 18 and over.
The coronavirus reproduction number, or R value, in England remains unchanged from last week and is between 1.2 and 1.4, according to the latest Government figures.