More than a million more people face fresh curbs on socialising and millions more could follow as Covid-19 cases double every week across the country.
The crucial R number has now risen to between 1.0 and 1.2 across the UK – meaning the virus is spreading.
Some 1.6million residents of Birmingham and neighbouring Sandwell and Solihull will be banned from socialising with people outside their own households from Tuesday after the city recorded the country’s third-highest rate of new cases.
And Liverpool was added to the Government’s watch list after a fourfold rise in confirmed cases there in the last fortnight.
A total of 3,539 new cases were recorded across the UK today, after 2,919 on Thursday and 2,659 on Wednesday.
Cases are doubling about every seven or eight days, according to experts at Imperial College London.
They found infections are rising in all age groups except the over-65s, and no longer clustering in hospitals or care homes – suggesting the virus is circulating more widely since lockdown was eased.
Around one in 1,400 people in England had coronavirus last week, the Office for National Statistics estimated.
Yvonne Doyle, medical director of Public Health England, said: “Although younger people continue to make up the greatest share of new cases, we’re now starting to see worrying signs of infections occurring in the elderly, who are at far higher risk of getting seriously ill.
“This is a reminder of the ongoing risk as the virus spreads throughout the UK.
“People should continue to follow social distancing rules, wash their hands regularly and wear a face covering in enclosed spaces. You shouldn’t mix with others when unwell.”
Birmingham recorded 975 new cases in the seven days to September 7, a rate of 78.2 per 100,000. Only by Bolton and Sunderland had higher rates.
West Midlands Metro Mayor Andy Street said Birmingham, Sandwell and Solihull “will now be escalated to an area of national intervention”.
He added: “The ban will take effect from Tuesday, but residents are advised to avoid household mixing before then as it has been identified as one of the drivers of transmission.
“To emphasise, this is about mixing between households, it is not about prevention of schools, workplaces, transport, any of the other options.”
Liverpool Metro Mayor Steve Rotheram said: “Over the past week we have seen a rapid increase in coronavirus cases across the Liverpool city region.
“We are not yet at the stage of having extra restrictions imposed on us, as other areas have, but if we continue on our current trajectory it will become a case of when, not if this happens.”
Sefton Council leader Ian Maher said all of Merseyside had been added to the watch list.
He added: “It’s essential that every single one of Sefton’s residents and businesses continue the great efforts they have made already to prevent us going into lockdown.”
Face coverings will be made compulsory in shops and other indoor spaces in Wales from Monday and indoor gatherings will be limited to up to six people.
First Minister Mark Drakeford said: “We have, I believe, a short window to get us ahead of a gathering storm.”
The fresh measures follow months of delay to the NHS contact tracing app, which will finally be rolled out in England and Wales on September 24.
The Government was forced to ditch its custom-made app to track the spread of the virus in June because it did not work on most Apple iPhones.
A new version based on a model developed by Google and Apple has been trialled on the Isle of Wight, in Newham, East London, and by NHS Volunteer Responders.
Health Secretary Matt Hancock said: “The launch of the app later this month across England and Wales is a defining moment and will aid our ability to contain the virus at a critical time.”
But Labour lashed the Government’s test-and-trace failings. Shadow Health Secretary Jonathan Ashworth said: “At the start of summer we warned an effective test, trace and isolate regime was needed ahead of the autumn. Rather than following our advice ministers have created a fiasco in testing and contact tracing.
“It’s now urgent an effective locally led public test, trace and isolate service is put in place to drive infections down and keep people safe.”
Residents in Lancashire booking online for coronavirus tests were directed to the Highlands of Scotland 300 miles away.
Blackburn with Darwen Councillor Maureen Bateson was told to travel 295 miles to Kingussie when she tried to book a test online.
The TUC warned many firms are not doing enough to protect workers after a poll found less than half of employees said their workplace had introduced social distancing. One in four low-income workers said employers had taken no action to reduce infection risk.
TUC chief Frances O’Grady said: “Ministers should crack down on bad bosses who risk their workers’ lives.”
A probe found the Department for Work and Pensions had “insufficient” social distancing at its Leeds office, where leaked messages suggested there had been at least two staff infections.
The nationwide ban on more than six people meeting has killed off the office Christmas party, the hospitality industry warns.
The British Beer & Pub Association called for a cut in beer duty and an extension of business rates relief if pubs were to survive.