The reproduction rate of coronavirus (R number) has risen above 1 in parts of England, but has remained constant in the UK as a whole, a briefing by the Scientific Advisory Group for Emergencies (Sage) has revealed.
The group, which advises the government on its Covid-19 response, said the R number in England was estimated to be between 0.8 and 1 - a marginal increase.
Sage also published regional values for R in England for the first time, with the South West having the highest range at 0.8-1.1.
But despite a relaxation of lockdown, the estimation for the UK as a whole remains below one - between 0.7 and 0.9 - which means the spread of the virus is decreasing.
Last week Sir Patrick Vallance, the government's chief scientific adviser, told journalists the value for England was between 0.7 and 1, admitting there was "a bit of regional variation".
The East of England is at 0.7 – 0.9, London, the Midlands, the North West and the South East at 0.8 – 1.0, and the North East and Yorkshire at 0.7 – 1.0.
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If the figure tips above one it means each person with Covid-19 will infect more than one other person with the virus, causing the spread to increase.
But experts cautioned against the use of regional R values – the average number of people an infected to pass the disease on to – saying that as the number of infections falls, regional R values become less reliable.
Instead, from next week the Government will publish the growth rates for regions that are based on data and make fewer assumptions.
Boris Johnson said there are "complex issues about the risks the whole of the community faces" regarding the R value, with 80% of infections existing in care homes or nosocomial infections within the NHS.
"The crucial thing is really the overall rate of infections that we're seeing, the overall rate of infections in the country, in the community, the rates of new hospital admissions are very important, and that's when we'll make the judgement," on whether to relax lockdown further, he said.
Before relaxing lockdown further, the government says there must be "reliable data from Sage showing that the rate of infection is decreasing to manageable levels across the board".
The latest update from Sage suggests the rate of infection is not falling in every region of the UK, putting step three for relaxing lockdown in jeopardy.
On July 4 the government hopes to reopen the hospitality industry, so long as the "five tests" - including a falling rate of infection - and are being met.
Crucial to the reopening of pubs, restaurants and bars, many in the industry say, is a reduction of the two metre social distancing rule.
They say a two-metre safe distance would make their business unviable, while reducing it to one metre would make a huge difference.
Many businesses in the industry say they'd need three weeks to make their premises "Covid-secure", but with July 4 just a month away they will be hoping for progress in the government's aim of reducing the R number.
The prime minister said at the moment "two metres is right" but "we're working with the scientists to work out a moment when the numbers [of infection] are down so far that we can really say that the two metre rule is no longer necessary".
He said the government is keeping the two metre rule "under review" and "obviously as we make further progress I hope to say more".
Sir Patrick has said with ONS figures on Friday showing the number of people with new infections is still declining, and thus less chance of catching it, it may influence political decisions to lower the distance.
Figures from the ONS show coronavirus mortality rates fell by more than half in all but two regions in England and Wales between April and May.
After increasing between March and April, age-standardised mortality rates fell in all regions by more than 50% except the North East and Yorkshire & The Humber, the Office for National Statistics (ONS) said.
The greatest decrease was in London, where the mortality rate fell by 83.3%.
The R number (rate of infection) explained:
Last week scientists at the University of Cambridge warned the R number was above, or at one, in some regions of the UK.
The MRC Biostatistics Unit at Cambridge University - a body which helps Public Health England model and forecast coronavirus infections - estimated the number to be 1.01 in the North West and 1 in the South West.
The government however has repeatedly insisted, since the first lockdown relaxations, that the number for the UK has remained below one.
It says the Cambridge MRC Biostatistics Unit is one of several groups which models for the government and, when considering all models, the national number is below one.