The measures have been imposed across England and will replace the only recently introduced three-tier “traffic light” system.
Mr Johnson had previously said that a short, sharp lockdown or “circuit breaker” as recommended by scientific advisers and such as the kind imposed in Wales, would not be necessary.
The U-turn to a second national lockdown came after scientific forecasting that suggests the winter death toll could surpass the 85,000 mark that had been predicted by government modelling in a worst-case scenario.
Mr Johnson said, “our hope was that by strong local action, strong local leadership, we could get the rates of infection down where the disease was surging”, but that “the virus has been spreading even faster than the reasonable worst-case scenario of our scientific advisers”.
The new measures have enforced the closure of much of the hospitality industry, including pubs and restaurants, however takeaways and deliveries are still permitted.
Essential shops, such as supermarkets, and educational settings, including nurseries, schools and universities, will remain open. Outdoor exercise is also allowed, while foreign travel has been banned.
The measures will remain in place until 2 December.
Here’s everything we know about what people can and cannot do in light of the new guidance.
Visiting friends and family
The new rules mean there will be no mixing of people inside homes anywhere in the country, except for in cases where childcare and other forms of support are necessary.
However, under the new lockdown, unlike the first in March, you can exercise or visit outdoor public places with the people you live with, your support bubble, or one person from another household.
Outdoor public places include parks, beaches, countryside, public gardens, allotments and playgrounds. You cannot meet in a private garden.
Single-adult households are still be permitted to form or maintain a support bubble with another household.
If you are clinically vulnerable or over the age of 60, the prime minister said you must minimise contact with other people as much as possible.
Schools and universities
There is another key difference between this and the first national lockdown: schools, colleges and universities are allowed to stay open.
During his speech, Mr Johnson said: “My priority, our priority, remains keeping people in education – so childcare, early years settings, schools, colleges and universities will all remain open.
“We cannot let this virus damage our children’s futures even more than it has already. I urge parents to continue taking their children to school and I am extremely grateful to teachers across the country for their dedication in enabling schools to remain open.”
In March, only vulnerable pupils and children of key workers were permitted to attend school in person, with A-levels and GCSE exams being cancelled nationwide.
Pubs and restaurants
However, establishments are permitted to open to offer takeaway food. Takeaway of alcohol is also allowed from pubs so long as customers order in advance and do not enter the premises.
All non-essential retail has been forced to close, including clothing and electronics stores, vehicle showrooms, travel agents and betting shops.
The government website states that auction houses, tailors, car washes, tobacco and vape shops must also shut. However, it adds that non-essential retail can remain open for delivery to customers and click-and-collect.
During his speech, Mr Johnson said: “I’m afraid non-essential shops will all be closed – though click-and-collect services can continue and essential shops will remain open, so there is no need to stock up.”
Supermarkets can remain open as usual throughout the duration of the four-week lockdown.
This includes food shops, supermarkets, garden centres and certain other retailers providing essential goods and services. The government has asked all essential retail to follow Covid-secure guidelines to protect customers, visitors and workers.
Exercise and outdoor sport
Just like the first lockdown, outdoor exercise will be allowed and encouraged, with people permitted to meet up with one other person from a different household for walks and exercise.
However, indoor and outdoor leisure facilities such as bowling alleys, leisure centres and gyms and sports facilities have been asked to close.
This includes venues such as swimming pools, golf courses and driving ranges, dance studios, stables and riding centres, soft play facilities, climbing walls and climbing centres, archery and shooting ranges, water and theme parks.
While travel within the UK is discouraged, people are allowed to do so for work purposes.
The new rules mean that people are expected to work from home if they can do so, with the government also advising people to avoid taking public transport if at all possible, not just because services are currently limited, but because doing so will make it easier for you to maintain social distancing.
Industries such as manufacturing and construction are also encouraged to keep running.
“Public sector employees working in essential services, including education settings, should continue to go into work,” the government website states.
“The risk of transmission can be substantially reduced if Covid-secure guidelines are followed closely. Extra consideration should be given to those people at higher risk.”
Parents can still access some registered childcare such as in-home nannies and babysitters and other childcare activities where reasonably necessary to enable parents to work, or for the purposes of respite care.
Early years settings can remain open and parents are able to form a childcare bubble with another household for the purposes of informal childcare, where the child is 13 or under.
Some households can also benefit from being in a support bubble, which allows single adult households to join another household.
Some youth services may be able to continue, such as youth work and support groups, but most youth clubs and groups will need to cease for this period.
All religious services have been stopped once more under the new guidelines. However, private prayer can continue.
All places of worship have been asked to close, unless they are being used for funerals, to broadcast acts of worship, individual prayer, formal childcare or where part of a school, essential voluntary and public services, such as blood donation or food banks, and support groups.
Weddings, civil partnership ceremonies are not permitted to take place except in exceptional circumstances.
Funerals can be attended by a maximum of 30 people, and it is advised that only close friends and family attend.
Linked ceremonial events such as stone settings and ash scatterings can also continue with up to 15 people in attendance and anyone working is not included.
Social distancing should be maintained between people who do not live together or share a support bubble.