England’s R number remains unchanged this week and sits between 1.2 and 1.4, according to government scientists.
This week approximately every 10 people infected with coronavirus will pass the virus on to between 12 and 14 others.
The figure, released weekly by the scientific advisory panel SAGE, was the same seven days ago.
It comes as Public Health England revealed cases of the Delta variant were up 79 per cent in one week.
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 risen, though most of those needing treatment have not had a vaccine.
The 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 per cent, 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 per cent 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.