Boris Johnson is facing calls for clarity after placing the UK on a police-enforced lockdown with drastic new measures in the fight against the coronavirus outbreak.
The Prime Minister ordered people only to leave their homes under a list of "very limited purposes", banned public gatherings of more than two people and ordered the closure of non-essential shops.
But police chiefs warned of phone lines being inundated with calls on Monday night with questions about what movements are still permitted, while MPs also called for answers.
In an address to the nation from Downing Street, Mr Johnson ordered people to only leave their homes to shop for basic necessities "as infrequently as possible", and to only perform one form of exercise a day.
They can also seek medical help, provide care to a vulnerable person or travel to work if "absolutely necessary", under the measures to last until at least Easter Monday.
"That's all – these are the only reasons you should leave your home," he said.
"You should not be meeting friends. If your friends ask you to meet, you should say no. You should not be meeting family members who do not live in your home."
A failure to follow the rules could see police dispersing gatherings and imposing fines, which Government officials said would start at £30.
After the UK death toll hit 335, the PM ordered the immediate closure of non-essential stores including those selling electronics and clothing.
All public gatherings of more than two people – other than those they live with – will be barred, the PM said.
Other premises to join pubs and restaurants in being closed are libraries, playgrounds, outdoor gyms, places of worship and hotels.
Parks will remain open for exercise, but all social events including weddings and baptisms will be stopped. Funerals can continue.
Mr Johnson said the measures will be "under constant review" and will be considered for relaxation in three weeks if the evidence allows.
Politicians who had piled pressure on the PM to enforce strict measures amid fears people were disregarding social distancing advice largely welcomed his announcement.
But there were calls for answers to the public's concerns after the PM scrapped his daily press conference on Monday to announce the measures in a statement.
Northamptonshire Police Chief Constable Nick Adderley warned the public not to "cripple our phone" lines with enquiries on the PM's announcement.
Lincolnshire Police warned of an "extremely high volume" of calls, and Humberside Chief Constable Lee Freeman said his force had received "a number of calls" on the subject which he said he was unable to answer.
Ken Marsh, chairman of the Metropolitan Police Federation, which represents officers in the capital, warned enforcement will be "very, very challenging" with "large amounts of sickness" already seen in the force.
"We will be dealing with it, but I'm not sure we will have the resources to be able to see it through," he told Sky News.
Labour leader Jeremy Corbyn said: "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."
Mr Johnson, who is to talk with his Cabinet on Tuesday, was also said to have prompted members of the public to call MPs to ask whether they should travel to work or not.
Online supermarkets appeared to buckle under the strain after the announcement, with crashes occurring on the Tesco, Sainsbury's and Asda websites.
Scottish First Minister Nicola Sturgeon said the measures that "amount to a lockdown" were "essential for the protection of all of us".
Forty-six more people died in England alongside four in Scotland and four in Wales on Monday, taking the number who have died in British hospitals after testing positive to 335. Those who have died in England range in age from 18 to 105.
In an earlier escalation of advice, Foreign Secretary Dominic Raab told citizens travelling overseas to return to the UK using commercial routes that are still running.
"If you are on holiday abroad the time to come home is now while you still can," he said.
Foreign Office staff are working to help citizens get back where routes have been halted due to the crisis.
Meanwhile, emergency legislation to tackle the outbreak cleared the House of Commons after MPs chose not to oppose the third reading of the Coronavirus Bill.