Mr Johnson had previously resisted pressure to introduce nationwide restrictions, saying they would be "disastrous" for the UK's finances and opting instead for a three-tiered system targeting local areas in England.
A member of the government's Scientific Advisory Group on Emergencies (Sage) warned Saturday that the virus is spreading far more widely than before.
Johnson had planned to announce the lockdown in Parliament on Monday but was forced into early action after the Times of London reported the news.
"From Thursday until the start of December you must stay at home, you may only leave home for specific reasons", Johnson said.
Mr Johnson made the announcement as coronavirus cases in the United Kingdom since the start of the outbreak passed one million, with a further 21,915 reported on Saturday. Britain's official death toll from the coronavirus is 46,555, the highest in Europe, with 326 new deaths announced Saturday.
It means that pubs, cafes, restaurants will shut except for takeaway and delivery services.
"No responsible prime minister could ignore the message of those figures", Johnson said.
Significant reduction in number of confirmed Covid-19 cases in Limerick
Globally, more than 4.59 crore people have been infected by the coronavirus and 11.9 lakh have died so far. DHHS advises that data is preliminary and is frequently updated as it is reported to the health department.
After talks with 16 regional prime ministers on Wednesday, Chancellor Angela Merkel announced measures to severely restrict the movement while keeping schools open and stimulating the economy.
A health expert says people coming into the country need to be quarantined and tested.
"The prime minister's got very, very hard choices to make, and I would encourage all members of the public and MPs to listen extremely carefully to what the prime minister says today and over coming days", Baker added.
For the first time since the pandemic began, more than 30,000 cases were reported on Friday.
A majority of Spain's 17 regions have already closed their domestic borders or will do so this week, preventing nonessential travel.
Targeted regional lockdowns will remain in force until after November 9, and cover consecutive bank-holiday weekends, which would typically lead to massive flows of travelers moving across the country.
The stay-at-home measures were lifted in June as cases dwindled, with Johnson declaring in July the country could see "a more significant return to normality from November.possibly in time for Christmas".
Regional authorities have extraordinary powers to declare curbs on movement after Prime Minister Pedro Sanchez announced a state of emergency on October 25. In Scotland, which has the U.K.'s lowest coronavirus infection rate, First Minister Nicola Sturgeon urged people not to travel across the border to England unless it was essential. A partial lockdown he unveiled Saturday is similar to neighboring Germany's, with schools and nonessential stores open and restrictions on staying home applying only at night.