Boris Johnson has tightened restrictions following a surge in infections in young people.
The most recent update from the Government means that people can no longer socialise in groups of more than six (the "rule of six").
The latest announcement could scupper the previous hope that the rules on social distancing could be lifted by the end of the year.
At a Downing Street press conference, the Prime Minister said: “In England we're introducing the rule of six. You must not meet socially in groups of more than six. And, if you do, you will be breaking the law."
Education settings and workplaces are unaffected by these new rules.
This replaces the existing guidance on allowing two households to meet indoors and the cap on 30 people.
Limited exemptions related to support bubbles larger than six will apply and hospitality settings and places of worship can take in more than six people overall.
The Telegraph has learned that ministers are considering imposing a national "curfew" after hospitality venues in Bolton were ordered to close between 10pm and 5am.
Below, we explain the existing rules in detail, but these do not currently apply to parts of England that are in local lockdown.
Read more: What parts of the UK are still in lockdown?
What about social distancing?
The "two household" rule, which allowed up to 30 people from two different homes to meet up, has been scrapped so that all family and social gatherings of more than six people, both indoors and outdoors, will be illegal under the "rule of six" in England.
The Government explained that "when meeting friends and family you do not live with (or have formed a support bubble with) you must not meet in a group of more than six, indoors or outdoors.
"This is against the law and the police will have the powers to enforce these legal limits, including to issue fines (fixed penalty notices) of £100, doubling for further breaches up to a maximum of £3,200."
Weddings, funerals, Covid-secure team sports, schools, workplaces and households or "support bubbles" that have more than six people in them will all be exempt.
The Government said people should "stay two metres apart from people you do not live with where possible, or one metre with extra precautions in place (such as wearing face coverings or increasing ventilation indoors)".
What about pubs?
Venues where people meet socially, such as pubs and restaurants, will now be legally required to request contact details of every member of a party and retain the information for 21 days. Fines of £1,000 could be levied against hospitality venues if they fail to comply.
Additionally opening hours of some venues could be restricted in some local areas. It comes after hospitality venues in Bolton were required to close between 10pm and 5am.
Pubs and restaurants etc can have more than six people in them, but they must not be in individual groups of more than six.
"Covid-secure marshals" will be introduced to help ensure social distancing in town and city centres in a bid to improve the enforcement capacity of local authorities
Read more: Could pubs close again?
When could social distancing end?
On September 9 the Prime Minister promised that the Government will work "round the clock" and that the UK will "beat this virus before too long".
However Boris Johnson admitted "it is just too early to say" where the UK will be by Christmas.
The Chief Medical Officer, Chris Whitty, clarified that the new restrictions are "not a very short-term thing" and it is hard to put an exact time limit on them.
Furthermore, scientists have cautioned that predicting an end to social distancing is difficult and depends on how much the one-metre rule influences the R number. Scientists also argue that the UK would need an effective test and trace system before social distancing could be lifted.
Social distancing may have to continue until there is enough immunity in the general population, according to Professor John Edmunds, from the London School of Hygiene & Tropical Medicine, which he says may only be provided by a vaccine.
“We will remain with some social distance measures in place until a safe and effective vaccine is found, mass-produced and delivered to the population,” Prof Edmunds said.
Can I see my family and friends?
Families and friends are allowed to meet in groups of no more than six - but there is a ban on hugging or touching.
It will mean a family of five will only be allowed to meet one grandparent at a time, while families of six or more will be banned from meeting anyone at all.
There is a limited number of exemptions including weddings, funerals, Covid-secure team sports, schools, workplaces and households or "support bubbles" that have more than six people in them.
Families will be told to choose one member to visit elderly relatives in care homes. Government guidance for the care sector – which bans flowers and hugs – says homes can begin allowing visitors shortly after they have undergone risk assessments of safety protocols.
The advice recommends "limiting the numbers of visitors to a single constant visitor per resident, wherever possible". It says: "This, for example, means the same family member visiting each time to limit the number of different individuals coming into contact."
Relatives will be told to wear face coverings and follow advice on social distancing as much as possible, keeping at least one metre away and avoiding handshakes, kisses or hugs.
Read more: Can I stay overnight and travel with family?
What is a support bubble?
On June 10 the Prime Minister announced that single-adult households - adults living alone, or single parents who have children under the age of 18 - would be able to form "support bubbles" with one other household.
"All those in a support bubble will be able to act as if they live in the same household, meaning they can spend time inside each other's homes and do not need stay two metres apart," Mr Johnson said.
He added that support bubbles must be exclusive, meaning that people cannot switch the house that they are in a bubble with, and cannot connect with multiple households. If one person in the bubble develops symptoms, all members will need to follow the advice on self-isolation for the following two weeks.
Anyone who is currently shielding due to medical vulnerability is not allowed to form or take part in a support bubble at this stage, but people who are currently shielding have been able to meet in groups from July 6.
And if the virus returns to dangerous levels up to 4.5 million people deemed to be at risk of serious illness from Covid-19 will be asked to stay at home or given tailored advice on protecting themselves.
For school children, primary schools are encouraged to have bubbles that include a whole class, while secondary schools are likely to need bubbles that consist of an entire year group so the full range of subjects can be delivered.
Older children will also be encouraged to keep their distance within groups of students and from staff.
What about grandparents?
On September 9, Mr Johnson said it "breaks my heart" to have to impose new restrictions on grandparents being able to meet their grandchildren.
"Of course I don't feel comfortable about it. It breaks my heart to have to insist on these restrictions upon individuals, upon families, grandparents," he told a No 10 news conference in response to a question from The Telegraph's Political Editor, Gordon Rayner.
He said the Government had been forced to act because some people had failed to follow social distancing guidelines.
"With the best will in the world people have not, I'm afraid, been totally following the guidelines," he said.
"I certainly don't want to blame people but now is the time for us to focus, to concentrate and to enforce the rule of six."