The UK has recorded the highest increase in Covid cases since February, with 8,125 new infections reported on Friday.
Official figures also showed there had been 17 more deaths, a worrying uptick from the single figure numbers recently reported.
The number of new cases reported in the 24 hours to 9am on Friday is the highest since February 26 when 8,523 infections were reported - more than three months ago.
The R rate represents the average number of people each Covid positive person goes on to infect.
When the figure is above 1, an outbreak can grow exponentially but when it is below 1, it means the epidemic is shrinking.
The latest figures from Public Health England (PHE), also published on Friday, show that 42,323 cases of the Delta variant first identified in India have been confirmed in the UK, up by 29,892 from last week.
Chairwoman of the All-Party Parliamentary Group (APPG) on Coronavirus, Layla Moran, said the figures should “set alarm bells ringing in Government”.
The Lib Dem MP added: “These figures should set alarm bells ringing in Government as we approach June 21.
“The Government must immediately explain to the public whether this exponential growth suggests the country is in line for a severe third wave, and if so what it is doing to prevent this.”
Meanwhile, Labour warned that the pace of the variant’s spread put the potential lifting of lockdown restrictions at risk.
Shadow home secretary Nick Thomas-Symonds said: “The pace at which cases of the Delta variant continue to rise is deeply worrying and is putting the lifting of restrictions at risk.
“The blame for this lies with the Prime Minister and his reckless refusal to act on Labour’s repeated warnings to secure our borders against Covid and its variants.”
Downing Street has defended its borders policy in relation to the Delta variant.
Meanwhile, a total of 59,032,003 vaccinations have now taken place in England between December 8 and June 10, according to NHS England data, including first and second doses, which is a rise of 422,093 on the previous day.
NHS England said 34,321,990 were first doses, a rise of 173,443 on the previous day, while 24,710,013 were a second dose, an increase of 248,650.
Data shows a total of 7,632,204 jabs were given to people in London between December 8 and June 10, including 4,664,676 first doses and 2,967,528 second doses.
This compares with 6,409,926 first doses and 4,810,225 second doses given to people in the Midlands, a total of 11,220,151.
The breakdown for the other regions is:
– East of England: 4,088,380 first doses and 2,970,921 second doses, making 7,059,301 in total
– North East and Yorkshire: 5,330,690 first and 3,911,351 second doses (9,242,041)
– North West: 4,334,415 first and 3,131,136 second doses (7,465,551)
– South East: 5,588,622 first and 4,054,617 second doses (9,643,239)
– South West: 3,623,411 first and 2,792,946 second doses (6,416,357)
Additional reporting by the Press Association.