Prime Minister Boris Johnson urged people to exercise responsibly when outside or 'new measures' will follow.
It came as deaths rose by 48 in the UK to 281.
Confirmed cases also rose to 5,683 out of 78,340 people tested.
The Prime Minister insisted that he did not want to close down access to parks and playgrounds because of the benefits to people’s mental and physical wellbeing.
But amid reports of crowds flocking to parks, beaches and beauty spots across the country, he said the Government was ready to impose the kind of “tougher” measures adopted in other European countries if people did not behave responsibly.
Meanwhile the NHS is to begin sending out letters to the 1.5 million people considered to be most at risk of the disease urging them to remain at home for the next 12 weeks.
At his daily No 10 news conference, Mr Johnson – who has faced criticism for not acting faster to slow the spread of the virus – said ministers had already closed down whole swathes of the economy, shutting pubs, clubs and restaurants.
He said the Government had always followed the scientific advice when it came to access to open spaces – but warned people needed to observe the guidance that they should not gather in groups and remain two metres apart.
“What they have always said so far is that the health benefits for the whole of society of keeping the parks and playgrounds open if we possibly can outweigh the epidemiological value of closing them,” he said.
“But of course looking at the way people behave and the way they are responding, we keep that under constant, constant review.
“If people can’t make use of parks and playgrounds responsibly, if they can’t do it in a way that observes the two-metre rule then of course we are going to have to look at further measures.
“The general principle should be that we should all as far as we possibly can stay home, protect our NHS and thereby save lives.”
