Media playback is unsupported on your device
Prime Minister Boris Johnson has said "we must act" to avoid another lockdown as virus cases rise in England.
He set out a new "rule of six" restricting gatherings to a maximum of six people, enforced with fines or arrests.
Mr Johnson also outlined a "moonshot" plan to control the virus with mass testing.
It comes as the UK reported another 2,659 coronavirus cases, the fourth day running of over 2,000 reported cases.
"I want to be absolutely clear, these measures are not another national lockdown. The whole point of them is to avoid a second national lockdown," Mr Johnson said.
He added "it breaks my heart to have to insist on these restriction".
The prime minister said the government was "working hard" to increase testing capacity to 500,000 tests a day by the end of October.
But he said they also want to use new types of test "in the near future" to identify people who do not have coronavirus and are not infectious so they can live life "in a more normal way".
He said these swab or saliva tests could be turned around in 90 or even 20 minutes, with millions processed each day - a "moonshot" effort to restore more normal life even if a vaccine or treatment is not available.
"We're hopeful this approach will be widespread by the spring and if everything comes together it may be possible - even for some of the most difficult sectors like the theatres - to have life much closer to normal before Christmas."
Outlining the new restrictions limiting all gatherings to six people, Mr Johnson said the government was "simplifying and strengthening the rules" after feedback from police and the public.
He said the restrictions would only be in place "as long as necessary".
"I'm sorry about that. I wish we did not have to take this step, but as your prime minister I must do what is necessary to stop the spread of the virus and save lives," he said.
The new "rule of six" means:
Social gatherings of more than six people in England will not be allowed in law from Monday 14 September The new rule applies to people in private homes, indoors and outdoors, and places such as pubs, restaurants, cafes and public outdoor spaces It applies to all ages The rule does not apply to schools and workplaces, or weddings, funerals and organised team sports A full list of exemptions is due to be published before the law changes People who ignore police could be fined £100 - doubling with each offence to a maximum of £3,200At present, the guidance says two households of any size are allowed to meet indoors or outdoors, or up to six people from different households outdoors. Until now the police have had no powers to stop gatherings unless they exceeded 30.
The number of people allowed to meet inside or outside varies in the UK's four nations. If you are meeting indoors: up to eight people from three different households can meet in Scotland; up to six people from two households in Northern Ireland; up to four households can form an "extended household" in Wales.