Here's an outline of what this third lockdown for England means:
Stay at home
Like the first UK lockdown in March, all residents of England must stay at home, only leaving home for work if it is impossible to work from home such as construction, manufacture or critical workers.
People can also leave home to provide voluntary or charitable services.
People can leave their homes to shop for necessities - for themselves or others - or to exercise locally once a day.
Exercise is permitted with one person from outside a household or support bubble. Social distancing must be maintained.
Overnight stays away from home are not permitted unless it is a person within a support bubble or you have a reasonable excuse. This means that holidays in the UK and abroad are not allowed, including staying in a second home or caravan.
Those extremely clinically vulnerable should stay at home as much as possible.
Other reasons permitting you to leave home include:
to provide care or help to a vulnerable person
medical appointments or care
Animal welfare (eg veterinary appointments)
Will schools, colleges and universities stay open?
From Tuesday, all schools will be closed and learning will be carried out remotely except for children of key workers or those that are vulnerable. Special schools will remain open.
University and college students will be expected to stay where they are and not return until at least mid-February. Nurseries will remain open.
What about support and childcare bubbles?
You can leave home to visit someone within your support bubble or to provide informal childcare for children under 14 as part of a childcare bubble.
People are also permitted to attend a support group of up to 15 people for respite care where that care is being provided to a vulnerable person or a person with a disability.
Will exams take place this year?
BTEC exams scheduled for the next few days will go ahead as planned.
As for GCSE and A levels, the government says there will be a discussion between the Office of Qualifications and Examinations Regulation (Ofqual) and the Department for Education about next steps.
However, it is expected that exams will not take place as normal this academic year.
In his address, Mr Johnson warned it would "not be possible or fair for all exams to go ahead as planned this summer".
Which shops have to close?All non-essential retail, hospitality and personal care businesses must close.
Restaurants can offer takeaway and delivery but are not allowed to serve alcohol.
What 'essential' shops can stay open?
Essential shops, that can remain open include:
Car repair shops
Market stalls selling essentials
Non-essential shops, that are required to close, include:
Personal care salons such as tanning shops and tattoo parlours
Entertainment venues such as cinemas, skating rinks and bowling alleys
Restaurants and other hospitality venues can continue with delivery or takeaway only, but people will not be able to add alcohol to any orders they collect.
Sports, leisure and worship
Other venues including zoos, golf and tennis clubs and outdoor gyms must close and team sports are not permitted.
However, elite sports will continue as will PE lessons and clubs for those children at school.
Places of worship will be permitted to open for socially distanced services and playgrounds will remain open.
Are weddings and funerals permitted to take place?
Weddings, civil partnership ceremonies and funerals are allowed to take place with strict limits on attendance.
A maximum of 30 people can attend funerals in Covid-secure venues. Other events such as commemorative events such as ash scattering can continue with up to six people in attendance. People working in the services are not counted in these limits.Weddings and civil partnership ceremonies can only take place with up to six people in attendance. Government guidelines say that weddings should only take place in exceptional circumstances, such as an urgent marriage where one of those getting married is seriously ill and not expected to recover, or is to undergo debilitating treatment or life-changing surgery.
Can I visit a relative in a care home?
The Government guidance says visits to care homes can take place only with “substantial screens, visiting pods, or behind windows”.
Close-contact indoor visits are not allowed and no visits will be permitted in the event of a Covid outbreak at a home.
What about international travel?
Only essential journeys abroad are permitted. Holidays abroad or in the UK are not allowed. People already on holiday should return as soon as possible.
Can I move house?
As per Tier 4 rules and similar to the first lockdown, people are permitted to move house.
People outside your household or support bubble should not help with moving house unless absolutely necessary.
Estate and letting agents and removals firms can continue to work. Property viewings are permitted.
Can cleaners and other workers come into my house?
As per previous rules, cleaners and tradespeople can enter your home.
Will furlough rules change?
On Tuesday, Chancellor Rishi Sunak announced that firms in the retail, hospitality and leisure industries - which will be closed - will receive a one-off cash sum worth up to £9,000 with the amount provided depending on the value of their business.
A further £594 million is also being made available for Local Authorities and the Devolved Administrations to support other businesses not eligible for the grants that might be affected by the restrictions.
Businesses should apply to their Local Authorities for the support.
It is estimated the latest raft of Treasury spending will cost £4.6 billion.
Are people who have been vaccinated exempt from lockdown rules?
No. Everyone in England, regardless of the Tier their area was in, must adhere to the new rules.
What happens if people break the rules?
The lockdown is being enshrined in law and police can take action if people leave home without a reasonable excuse.
The police can issue a Fixed Penalty Notice of £200 for the first offence, doubling for further offences up to a maximum of £6,400.