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 law change will ban larger groups meeting anywhere socially indoors or outdoors, the government 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, doubling on each offence 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 unaffected.
Prime Minister Boris Johnson is expected to give further details at a Downing Street news conference later on Wednesday.
What are the new rules for meeting my friends?
Previously, guidance in England allowed gatherings of up to six people from different households outdoors - or two households of any size, indoors or outdoors. But until now the police have had no powers to stop them unless they exceeded 30.
"One of the pieces of feedback we had including from the police was that we needed the rules to be super simple so that everybody knows what they are," said Health Secretary Matt Hancock.
"And now this will now be rigorously enforced by the police."
Mr Hancock told BBC Breakfast: "This is really simple. Gatherings are ok, they should be socially distanced of course, but groups only of up to six."
He said it means that some families will not be able to see both grandparents at the same time. "You know, I have three children," he said. "We have a family of five. And so we'll be able to see one other person at a time, as a whole family."
Mr Hancock was also asked about testing, after people with symptoms struggled to access testing in recent days.
"Unfortunately we have seen this quite sharp rise in the last couple of weeks of people without symptoms who don't have a good reason coming forward and getting a test," he said, saying 25% of people who were getting a coronavirus test were not eligible.
"I've even heard stories of people saying 'I'm going on holiday next week therefore I'm going to go get a test'. No. That's not what the testing system is there for."
At-a-glance: What are the new rules?
No 10 said any group of seven or more people gathering anywhere "risks being dispersed by police or fined for non-compliance".
BBC political correspondent Nick Eardley pointed out that pubs and restaurants would be allowed to have more than six customers inside, but that the groups of six would have to be socially distant from each other.
The rationale behind allowing this, but not allowing larger groups of people inside other people's homes, is that businesses can only be open if they follow safety and hygiene measures set out by the government, he added.
Downing Street said Mr Johnson held a virtual roundtable with police forces last week, and heard officers wanted clearer rules and enforcement on social contact.
A law change will ban larger groups meeting anywhere socially indoors or outdoors, the government 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, doubling on each offence 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 unaffected.
Prime Minister Boris Johnson is expected to give further details at a Downing Street news conference later on Wednesday.
What are the new rules for meeting my friends?
Previously, guidance in England allowed gatherings of up to six people from different households outdoors - or two households of any size, indoors or outdoors. But until now the police have had no powers to stop them unless they exceeded 30.
"One of the pieces of feedback we had including from the police was that we needed the rules to be super simple so that everybody knows what they are," said Health Secretary Matt Hancock.
"And now this will now be rigorously enforced by the police."
Mr Hancock told BBC Breakfast: "This is really simple. Gatherings are ok, they should be socially distanced of course, but groups only of up to six."
He said it means that some families will not be able to see both grandparents at the same time. "You know, I have three children," he said. "We have a family of five. And so we'll be able to see one other person at a time, as a whole family."
Mr Hancock was also asked about testing, after people with symptoms struggled to access testing in recent days.
"Unfortunately we have seen this quite sharp rise in the last couple of weeks of people without symptoms who don't have a good reason coming forward and getting a test," he said, saying 25% of people who were getting a coronavirus test were not eligible.
"I've even heard stories of people saying 'I'm going on holiday next week therefore I'm going to go get a test'. No. That's not what the testing system is there for."
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 people in England of all ages, and to gatherings indoors and outdoors, in private homes, public outdoor spaces, and venues such as pubs and restaurants.
No 10 said any group of seven or more people gathering anywhere "risks being dispersed by police or fined for non-compliance".
BBC political correspondent Nick Eardley pointed out that pubs and restaurants would be allowed to have more than six customers inside, but that the groups of six would have to be socially distant from each other.
The rationale behind allowing this, but not allowing larger groups of people inside other people's homes, is that businesses can only be open if they follow safety and hygiene measures set out by the government, he added.
Downing Street said Mr Johnson held a virtual roundtable with police forces last week, and heard officers wanted clearer rules and enforcement on social contact.
