The rate at which the Covid-19 virus is spreading appears to be speeding up.
The R number, indicating how fast the coronavirus epidemic is growing, has risen from 1.1-1.4 to 1.2-1.5.
An Office for National Statistics (ONS) survey estimated there were 9,600 new cases a day in England in the week to 19 September - up from 6,000 the week before and three times that being picked up by general testing.
It comes as more restrictions come into effect in parts of England and Wales.
On Friday, the daily number of positive cases in the UK picked up by coronavirus testing rose to a new high of 6,874, government figures show.
A further 34 deaths were announced, although figures were not available for Scotland because of a power cut at the National Records of Scotland.
Infection rates are highest in the north west of England and in London.
As infection rates rise, new restrictions are being brought into effect in the following areas:
- Cardiff and the county of Swansea will go into lockdown at 18:00 BST on Sunday - 24 hours after the Carmarthenshire town of Llanelli
- In Leeds, Stockport, Wigan and Blackpool different households will be banned from meeting in private homes or gardens from midnight on Friday
- London has been added to the government's Covid-19 watch-list, meaning all of its boroughs are now classed as "areas of concern" but will not yet have additional restrictions
An R or reproduction number above one means the epidemic is growing. It's a measure of how many extra people each coronavirus case is infecting,
In March, before any control measures were put in place, R was thought to be just under three.
The ONS's estimates of how much of the population is currently infected are based on testing a representative sample of people with or without symptoms.
It is different to the number published daily by the Department of Health and Social Care. That records positive cases in people with potential Covid symptoms who request tests.
And in the week up to 19 September, the DHSC data showed roughly 3,000 positive tests a day in England - a total of 23,378.
In contrast, the ONS survey suggest there were actually 103,600 people in England with the virus, equating to an estimated one in 500 people in private homes.
The number does not include cases in hospitals and care homes.
'Clear evidence' of increase
The ONS said there was "clear evidence" of an increase in the number of people testing positive for Covid-19 in all age groups, but rates are currently highest in those aged 17-24.
Infection rates are highest across the north of England and in London, with smaller increases seen in the Midlands.
In Wales, cases appear to have risen dramatically but because there are fewer people in the sample, there is a lot of uncertainty around the precise figure.
But central estimates suggest they could have risen almost seven-fold, from 1,500 people in total having Covid the previous week to more than 10,000.
The ONS has also begun surveying people in Northern Ireland, where early figures suggest one in 300 people had the virus in the period 6-19 September.
These figures only take us up to the end of last week, and as such may be an underestimate of the current situation.
Cases have been rising over the past few weeks, and have begun to translate to a rise in hospital admissions.
Data from the Covid Symptom Study app, run by King's College London and tech company ZOE, put the daily figure for England at 12,883 - higher than the ONS.
Its figures are based on people who download and use the app, so it is not a random sample - but does include a larger number of positive tests.
The ZOE figures are also more up to date than the ONS's and so may be capturing more recent rises.