With several areas expected to head into tier 3 in the coming weeks, we take a look at the rules and restrictions now being put in place to prevent further spread of the illness.
Under the new measures, areas in England are classified at medium, high or very high risk, and placed under restrictions of varying severity.
Under the highest tier, people living in the region will not be able to socialise with other people from outside their households in indoor settings.
What areas are in tier 3 of the new three tier Covid alert system?
The harshest measures in the United Kingdom have been imposed in the Liverpool City Region, which is now in the "very high" alert level, meaning bars, pubs and gyms have been ordered to shutter. "Pubs, bars, gyms and leisure centres, betting shops, casinos and adult gaming centres will all close".
The government sets a baseline for measures in these areas, and the rest are decided after consultation with local authorities.
Now only Merseyside - which includes Liverpool and the Wirral - has entered this alert level and local leaders have secured the closure of leisure facilities such as gyms, spas and casinos on top of the base measures.
The PM said all retail outlets, schools and universities will remain open.
To bring life back to normal, countries, such as Britain, China, Russia and the United States, are racing against time to develop coronavirus vaccines.
The new rules are to be debated by MPs in the House of Commons on Tuesday before coming into force from Wednesday, with a review of the system in a month's time.
The prime minister also pledged a further £1bn in financial support for local test and trace and local enforcement, as well as expanding the existing wage and business safety net.
The government has announced a support package to pay two-thirds of the salaries of employees of companies that are told to close, but many in the pub and restaurant sector say that is not enough to save already struggling businesses.
A three tier lockdown system has been introduced in England - here's your need-to-know on the "very high" tier three level.
In areas at high risk, members of different households are barred from meeting indoors.
He also claimed that permitting the virus to move through the younger population was not an option either due to the velocity of the virus, which would see older people hit too.
Boris Johnson ignored advice from the team of scientists who advise the government on its coronavirus response, according to newly published papers.
The researchers said analysing excess deaths from all causes combined - which they did using weekly death data from the 21 countries - gives a more comprehensive picture of the overall impact of a pandemic.
Main opposition Labour leader Keir Starmer meanwhile accused Johnson of "running to catch up with the virus that he has lost control over long ago".
Manchester intensive care consultant Jane Eddleston said 30% of critical care beds were taken up with COVID-19 patients and this was starting to affect healthcare for others.
50 further deaths have also been recorded, a decline of 15 from Sunday figures.
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