Prime Minister Boris Johnson said on Friday that the order would "put the country in a better and stronger position and we will be able to save thousands of lives".
The prime minister said nightclubs, leisure centres and theatres must also close their doors in an effort to reduce "unnecessary" social gatherings by 75%. The closures will be reviewed on a monthly basis.
"Some people may of course be tempted to go out... But please don't," he said.
"You may think you are invincible, but there is no guarantee you will get mild symptoms, and you can still be a carrier of the disease and pass it on to others."
Earlier on Friday, figures showed that the number of people who have died in the UK after contracting COVID-19 had risen to 177 after England saw 39 more deaths - the biggest rise in a day.
The UK also saw 714 confirmed cases of coronavirus diagnosed in a day, bringing its total number to 3,983.
In a bid to help the economy survive the pandemic, Chancellor Rishi Sunak announced the government would step in to pay people's wages, with grants that will cover 80% of the salaries of retained workers - up to £2,500 a month.
He urged businesses to consider government support before laying off employees.
He also said he would defer the next quarter of VAT payments for businesses until the end of June, in a £30bn injection into the economy.
Mr Sunak pledged £1bn for renters by boosting housing benefit and Universal Credit, and added that the welfare payments' "generosity" would be increased to allow the local housing allowance to cover at least 30% of market rents.
Reacting to the latest financial measures, shadow chancellor John McDonnell said: "It looks as though it's going to be weeks before it comes into action."
He told Sky News: "He [Mr Johnson] has shifted but I think he needs to go a lot farther and a lot faster.
"He's said 'whatever it takes' - this isn't whatever it takes, he hasn't gone far enough and I'm worried about yet another delay in getting these benefits to people, getting the wages in people's pockets."
But the chancellor's measures were largely welcomed by business and union leaders.
Also commenting on the massive rescue package, Sky's economics editor Ed Conway said: "I'm slightly dumbfounded. This is an enormous deal.
"It shows how desperately concerned they are about the state of the economy.
"This is a nuclear button for the government to press because clearly they are panicking that people are firing staff at an unprecedented rate.
"It will be really expensive. It depends on how long is goes on for. It is a very big move."
Many gym chains said they would freeze membership fees and deliver workouts online to help members keep fit.
PureGym, one of the UK's largest operators with 230 premises, told more than a million members they will not have to pay while gyms are closed, adding that it would launch a workout and well-being platform through its app.
Virgin Active and Nuffield Health both told customers that membership payments would be frozen and they would deliver workouts online.
David Lloyd Clubs, The Gym Group, DW Fitness First, Better Leisure Centres and Better Gyms also confirmed a payment freeze for members.
Huw Edwards, chief exceutive of not-for-profit fitness industry body ukactive, said: "Our members will continue to support their customers even though the physical facilities will be closed - adapting and finding innovative new ways to help people to maintain active lives.
"We will continue to keep our nation healthy and active in the most challenging of times.
"The fitness and leisure sector will reopen its facilities when it is safe to do so, and will do so with increased vigour and the energy that has always been its hallmark."