The legal limit will be reduced from 30 in the biggest coronavirus crackdown since lockdown rules were eased.
Social gatherings of more than six people will be illegal in England from Monday – with some exemptions – amid a steep rise in coronavirus cases.
A new legal limit will ban larger groups meeting anywhere socially indoors or outdoors, No 10 said.
But it will not apply to schools, workplaces or Covid-secure weddings, funerals and organised team sports.
It will be enforced through a £100 fine if people fail to comply with police, doubling up to a maximum of £3,200.
Several exemptions apply to the new rules – which come into force on 14 September – with households and support bubbles bigger than six people are unaffected.
A full list of exemptions will be published by the government later.
Prime Minister Boris Johnson is expected to deliver further details at a Downing Street news conference on Wednesday.
In a preview of his address, the PM said: “We need to act now to stop the virus spreading. So we are simplifying and strengthening the rules on social contact – making them easier to understand and for the police to enforce.
“It is absolutely critical that people now abide by these rules and remember the basics – washing your hands, covering your face, keeping space from others, and getting a test if you have symptoms.”
No 10 said any group of seven or more people gathering anywhere “risks being dispersed by police or fined for non-compliance”.
At-a-glance: What are the new rules?
- Social gatherings of more than six people in England will not be allowed in law from Monday 14 September
- The new rule applies to private homes, indoors and outdoors, and places such as bars and cafes
- 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 £3,200
The change applies to England only, to people of all ages, and to gatherings indoors and outdoors, in private homes, public outdoor spaces, and venues such as pubs and restaurants.
The devolved administrations in Scotland, Wales and Northern Ireland are able to set their own coronavirus restrictions and, while largely implementing similar rules, have moved at their own pace during the pandemic.
Downing Street said Mr Johnson held a virtual roundtable with police forces which heard officers wanted clearer rules and enforcement on social contact.
Previously, guidance in England allowed gatherings of up to six people from different households – or up to 30 people from two households.
Coronavirus infections are rising among young people
A spike in young people getting COVID-19 will result in more older people being admitted to hospital with the virus, scientists have warned.
The latest Public Health England (PHE) data found the 20-29 age group now has the highest coronavirus infection rate, with 28 people infected per 100,000 people in England in the week ending 30 August.
Over the summer, cases have risen faster in younger groups than any other, with cases tripling in the 20-29 age group at the end of August compared to the first week of July – when it reached its lowest point.
At the end of August, the rate in the 10-19 age group was four times higher than in the first week of July.
Dr Adam Kucharski, infectious disease epidemiologist at the London School of Hygiene and Tropical Medicine, said it could be just a few weeks until the UK sees an increase in older people being admitted to hospital after the spike in young people testing positive.
He told Sky News: “We’ve seen lots of changes in behaviours recently, more people are gathering now and in younger groups especially, more people are happy to gather.”