Boris Johnson’s official spokesman has said the government “won’t hesitate to take further measures” to enforce social distancing if evidence shows that advice is being ignored.

The comment came amid widespread calls for tougher restrictions after thousands of people took advantage of the sunny weather over the weekend to congregate at parks, beaches and outdoor markets, with fears that many were failing to observe guidance to keep two metres apart.

Labour today called for the government to move to enforced social distancing “as a matter of urgency”.

And Scottish first minister Nicola Sturgeon said that advice on limiting social contacts to slow the spread of coronavirus should not be regarded as optional, but as “rules we are expecting people to comply with”.

Ms Sturgeon said she would use emergency powers to enforce the guidance within a few days, and issued a plea to shops selling anything but food and medicine to “close now”.

Meanwhile, the professor of public health at Imperial College, London, Helen Ward, said a "national lockdown" was needed now to save lives.

Prof Ward told Radio 4's World at One: "I know it's a frightening word, but we absolutely have to stop non-essential travel, non-essential business and activities. We have to enforce social distancing.

"We need to clear the streets, the buses and trains of non-essential travel and activities. There are people who need to get to work - health workers and other critical workers. They need to be able to use the Tube without being crammed in with no opportunity for that two-metre distance. Other people do not need to be out there."

There was no evidence to suggest that the UK could avoid the levels of disease seen in Italy unless it took tougher measures, said Prof Ward.

"Everything points to the fact that if we don't have these stringent measures now, we will continue to see a steady growth in the number of cases," she warned.

Health secretary Matt Hancock indicated that tougher measures were under consideration.

Asked whether the Cabinet would be considering a firmer lockdown when it meets on Tuesday, Mr Hancock told Radio 4's Today: “Nothing is off the table. Of course we are looking at what other European countries are doing.”

Mr Hancock said he did not know why some people were ignoring the Government’s advice.

“It’s very selfish,” he said. “The NHS is doing everything it can and preparing for the spread of this virus.

“If people go within two metres of others who they don’t live with then they’re helping to spread the virus – and the consequences of that costs lives and it means that, for everyone, this will go on for longer.”

The prime minister’s spokesman told a Westminster briefing that no decision had been taken to move to a mandatory lockdown or to require the closure of non-essential shops.

But he added: “We are getting data all the time and discussions are taking place all the time. If we do need to take further measures, we won't hesitate to do so and to do so quickly.”

The spokesman said the government had sent out a clear message: “People should stay at home if possible. This will save lives, protect the vulnerable and support the NHS.

“If people are going out socialising when they don’t need to, they are putting people’s lives at risk.

“If information we are gathering shows that social interaction hasn’t stopped as we hoped it would, then we will need to take further measures.”

The spokesman said he "did not recognise" reports that Mr Johnson was facing the threat of "mutiny" from senior ministers and officials if he does not move imminently to a compulsory lockdown.

Shadow health secretary Jonathan Ashworth said that the time for tighter restrictions has now come.

"Labour will continue to try to support the government’s response to the coronavirus emergency as best we can," said Mr Ashworth.

Jonathan Ashworth (BBC)

"But after another weekend of apparent public confusion and widespread non-compliance with 'social distancing', of grave scientific warnings and brave medical professionals talking of being sent to work like 'lambs to the slaughter' with inadequate protective equipment, something has to change.

"Other countries have taken further far-reaching social distancing measures. We now call on the government to move to enforced social distancing and greater social protection as a matter of urgency.

"The Prime Minister must outline further necessary steps the government will now take to keep people safe, protect our NHS and save lives."

In a message to people in Scotland, Ms Sturgeon said: “Life should not be carrying on as normal right now. Life should not feel normal for you right now.

“If it is, then you are not doing the right things, and I want to ask you today to please put that right.”

Ms Sturgeon said that emergency powers to enforce coronavirus advice would become available to her within a few days, adding: “We will use them.”

But she added: “Nobody should rely on that. Please do the right thing now.”

Hammersmith and Fulham Council in south London moved to shut down its parks on Sunday after seeing them thronged with people over the weekend.

Council leader Stephen Cowan told Radio 4’s World at One: “Understandably, it’s very hard for people to come to terms with the changes in their lives they are going to need to make with this contagion, but it’s a very serious problem.

“We took the view that every time they met each other and failed to follow social distancing measures, they were passing on the contagion to different people.

“We’d asked our parks police to encourage social distancing, but every time they did it they were putting themselves at risk and it wasn’t working.”

Meanwhile, a group of 47 Labour MPs wrote to Mr Johnson to demand “more stringent measures” to ensure that people stay at home where possible and the closure of all except “vital” shops.