The coronavirus transmission rate in the UK has risen to between 1.2 and 1.5, government advisers have said.
Last week, the government's Sage committee said the R number was estimated to be between 1.1 and 1.4.
The number is a measure of the number of people that one infected person will pass the virus on to, on average.
The higher R is above 1, the faster the epidemic is growing.
It comes as new data shows the estimated number of cases of coronavirus across England has jumped 60 per cent in one week.
Meanwhile London has been placed on the national Covid “watch list” as an area of high concern.
There were around 9,600 new coronavirus infections per day in England between September 13 and 19, up on 6,000 the week before, according to the Office for National Statistics (ONS) infection survey.
The survey, which tests thousands of people in English homes whether they have symptoms or not, found an estimated 103,600 people had Covid-19, equating to around one in 500 people.
The ONS said: “The estimate shows the number of infections has increased in recent weeks.
“In recent weeks, there has been clear evidence of an increase in the number of people testing positive for Covid-19 in all age groups, with the current rates highest in the 17 to 24 age group.
“There is evidence of higher infection rates in the North West, Yorkshire and the Humber, London and North East.”
In London, 620 new cases were confirmed in the last 24 hours – more than double the number at the start of the week.
Thirty-five more patients with Covid were admitted to hospital in the last 24-hour period, taking the total in the capital's hospitals to 212, of which 40 are on ventilators.
A formal confirmation of London's place on the Covid "watch list" is due this afternoon from Public Health England but the announcement was made this morning by London Councils, which represents the 33 boroughs.