Leeds was set to become the latest English city to have extra coronavirus restrictions imposed as cases continued to rise.
Officials in the city announced an expected ban from midnight on households mixing in each others' homes, ahead of confirmation from the Department of Health and Social Care.
The latest seven-day Covid-19 rate in Leeds was found to be 98.5 per 100,000 people, with an 8.4% positive test rate.
That meant Leeds was likely to be added to the Government's list as an "area of intervention", reporters were told at a joint news conference with the council leader, its chief executive and the director of public health.
Councillor Judith Blake, leader of Leeds City Council said: "We are acutely aware that nobody wants to see further restrictions placed on life in Leeds and alongside our partners we have been doing absolutely everything within our power to avoid that.
"But the safety of the city and the public simply has to come first and we have now reached a point where we all need to take additional steps to contain the spread of this terrible virus within our communities.
"How long these new measures last and how much further they may need go in the coming weeks and months will depend on everyone playing their part."
Victoria Eaton, director of public health, said: "Any restrictions on seeing the people close to you are incredibly difficult to take but these rules have been put in place to protect families, friends and neighbours from a virus which is spreading at a dangerously rapid rate.
"It's vital that we all play our part in containing that spread by sticking to the latest rules and guidance and ensuring that we don't put ourselves or each other at unnecessary risk."
Tom Riordan, council chief executive, said: "What we are trying to do is give a simple message – you shouldn't really mix with other households."
He said about 780,000 people will come under the new measures which could be in place through the winter.
The addition of Leeds' population would take the number of people living under local restrictions to more than 16.2 million people across the UK.
Mr Riordan added: "I think we know from the experience of Leicester, Greater Manchester and West Yorkshire that when these restrictions are brought in they do not tend to be lifted after a week or two."
He said it was expected that it would become law that from midnight households should not mix inside or in the garden, and that in pubs, restaurants and in public spaces, it would be strong advice that that should not happen.
Meanwhile, London is being made an "area of concern", according to London Councils, a cross-party organisation which represents all 32 boroughs and the City of London.
No additional measures will be taken in the city but testing capacity will be boosted to closely monitor the growth of the virus.
In a statement, London Councils urged residents to follow the new Government restrictions introduced on Thursday and said rising cases were a "stark reminder that now is time for all Londoners to pull together and take action to keep themselves, their families and their communities safe, and to ensure that London's economy is protected".
It added: "London boroughs are working with their communities, business and the police to engage, educate, explain and, if necessary, enforce the new restrictions and regulations, and the Government must ensure that it funds these so resources do not need to be drawn from other services.
"We ask all Londoners to work together and abide by the national restrictions announced on Tuesday."
In Wales, Cardiff and Swansea will go into local lockdown from 6pm on Sunday, the Welsh Government confirmed.
Under the restrictions, people will not be able to enter or leave the areas without a reasonable excuse.
They will not be able to meet indoors with anyone they do not live with, with extended households suspended.
People must work from home when possible, health minister Vaughan Gething told a press conference in Cardiff.
The town of Llanelli will go into local lockdown on Saturday at 6pm.
Restrictions are already in force across large swathes of North West England, West Yorkshire, the North East and the Midlands, as well as parts of West Scotland.