Boris Johnson announced earlier tonight that he is bringing in strict new measures in a bid to halt the spread of coronavirus.
But it is believed the draconian measures, which will be reviewed in three weeks' time, will help slow the spread of Covid-19 and ease the growing pressures on the NHS.
Labour leader Jeremy Corbyn said: "The Prime Minister is right to call for people to stay at home, protect our NHS and save lives."
He added: "This is the right response to the coronavirus pandemic, and one we have been calling for.
"There now needs to be clear guidance to employers and workers about which workplaces should close - and the Government must close the loopholes to give security to all workers, including the self-employed, as well as renters and mortgage holders.
"We welcome these moves and will be working to ensure everybody has the protection and security they need."
And Labour's Mayor of London Sadiq Khan said in a video posted to Twitter: "I want to speak directly to Londoners: these rules are not optional.
"These instructions have been put in place to stop the spread of the virus and must be followed at all times to save lives."
He added: "These unprecedented circumstances call for extraordinary measures. Unless we follow these rules, people will die."
Scotland's First Minister Nicola Sturgeon said new coronavirus restrictions "amount to a lockdown".
"I am not going to sugarcoat it in any way," she said. "Coronavirus is the biggest challenge of our lifetime."
She said the new measures are "not done lightly".
"Stay at home," she said. "That is the message I gave yesterday and I am reinforcing that message now."
The Liberal Democrats added: "Many people will be anxious about the steps the government has taken, but it's the right decision to restrict our normal way of life to tackle this crisis.
"We urge people to play their part #StayAtHomeSaveLives."
While Brexit Party leader Nigel Farage struck a more downbeat tone, saying: "So we are to be locked down - and a new testing regime will begin.
"Will the planes keep coming from Milan, Tehran and Beijing?
"I expect so. It's all too late."
And the government's Health Minister Nadine Dorries, who was the first MP to be diagnosed with coronavirus, tweeted: "Please do as the PM asks. This is about saving peoples' lives.
"There is nothing more important. The PM mentioned the police.
"We really don't want to go there. Please, please, #StayAtHomeSaveLives."
A call that was echoed by former chancellor Sajid Javid, who famously quit government earlier this year in a row with Boris Johnson.
He said: "This could not be more serious. Please stay at home to save lives."
And Mr Javid wasn't the only former political rival to support the PM.
Former health secretary Jeremy Hunt, who previously criticised the speed of the Government's efforts to shut down the movement of people, tweeted: "This is absolutely the right decision by @BorisJohnson.
"It takes 2-3 weeks before these measures likely to feed into the rate of new infections but at last we have hope the tide will now start to turn. Massively ramping up testing is the next vital step."
Green Party co-leader Jonathan Bartley also took to social media to react.
He tweeted: "Not soon enough but a welcome announcement from the Prime Minister.
"More guidance is now needed on the detail and should be provided quickly for the many people who are fearful and will have
questions about the way this applies to their own situations - as well as on enforcement."
Not everyone was impressed with the Prime Minister's decision.
Labour MP Neil Coyle tweeted: "If there's no support for self-employed people and no penalties for employers insisting workers come in, Johnson's announcement is insufficient to ensure compliance.
"He's acted late and the broadcast also sadly seemed like an apology for the ensuing NHS crisis in advance."
Labour's shadow security minister Nick Thomas-Symonds also raised concerns over mental health aspects of the Coronavirus Bill - including a person being detained on the say-so of a single doctor.
He described this as a "significant change" while Conservative former minister Andrew Mitchell intervened to ask: "Is he also saying once the immediate crisis is over, anyone who has been sectioned under that regime should be immediately the subject of the existing regime?"
Mr Thomas-Symonds replied: "Yes, absolutely."
Labour former minister Kevan Jones said he understood the pressures on doctors and suggested having one sign it off but with a requirement for a second to review the case within a certain number of days.
