Communities secretary Robert Jenrick hinted a lockdown could be enforced to stop the spread of coronavirus, amid fears people are ignoring advice on social distancing.
The cabinet minister warned the public that advice on social distancing “isn’t a game” and the government will be forced to consider “other options” if people continue to flout new rules.
It could see the police enforcing rules on self-isolation and social distancing.
Boris Johnson ordered pubs and restaurants to close this week and asked the public to stay at home and away from others.
The vulnerable - including people aged over 70, pregnant women and those with existing health conditions - should strictly self-isolate for three months, the prime minister also said, as he underlined the measures were vital in order to save lives from the potentially-fatal disease.
But despite this, reports have emerged of crowds flocking to beaches and families mixing closely at parks.
Speaking to Sky News, Jenrick said children should not be going to play dates and that, while it was OK for people to go outdoors and exercise, they should be avoiding crowds and keeping their distance.
“Lots of people sat out together in parks or on beaches. That isn’t sensible. We strongly discourage that,” he said.
He added that if people continued to ignore advice, the government would take further action, he said, suggesting the police could be asked to intervene.
It comes as emergency legislation to tackle the disease is set to include powers for the police to arrest people who refuse to isolate themselves.
Jenrick said: “We want to live in a free society where we can continue to go about activities whilst following the medical advice. But this isn’t a game, it is very serious.
“People need to follow that advice. If people don’t follow that advice then clearly we’ll have to consider other options, but none of us want to go down that route.”
GPs have identified 1.5m people who are particularly vulnerable to the virus and will be receiving a letter from government imploring them to follow the advice for 12 weeks.
He also stressed that these people would be guaranteed food supplies.
London mayor Sadiq Khan, meanwhile, urged people in the city to follow the advice and stay at home.
The city is ahead of other parts of the country in the spread of the virus, with a majority of cases emerging there.
The UK death toll on Sunday rose to 240, after a further seven patients in Wales died.
Labour leader Jeremy Corbyn also spoke to Sky News urging people to follow health advice.
He said: “We are all the front line now and I do urge people to listen, listen, listen to the advice you’re given.
“Don’t closely associate with people, don’t go places where there’s going to be big crowds, make sure you’re not part of a big crowd.”