BORIS Johnson has said the Government is ready to impose tougher restrictions to curb the spread of the coronavirus if people do not follow the guidance on social distancing.

His warning came as the latest official figures showed the number of people across the UK who have died after testing positive for Covid-19 has risen by 48 to 281 – including an 18-year-old, thought to be the youngest victim so far.

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."

He added: "I don't think you need to use your imagination very much to see where we might have to go, and we will think about this very very actively in the next 24 hours."

The Government later issued updated guidance on essential travel, saying it did not include visits to "second homes, camp sites, caravan parks or similar, whether for isolation purposes or holidays".

Earlier, in a message to the nation, the Prime Minister warned Britain was only "two or three" weeks behind Italy where the death toll has already risen above 5,000 making it the worst outbreak anywhere in the world.

He said that unless the UK could control the spread of the virus through social distancing, the NHS would be "overwhelmed" in the same way that the Italian healthcare system had been.

However the deputy chief medical officer for England, Dr Jenny Harries, cautioned against comparing the UK's figures too closely with other countries'.

"As you go through a sharp rise in numbers, which we will see going forward, you have to be careful to be comparing too precisely," she said.

"We will look back in due course, sadly, and see the true number of people who have died from coronavirus."

Elsewhere other political figures adopted a notably more strident tone than the Prime Minister as they warned people not to leave their homes other than for essential business.

London Mayor Sadiq Khan, whose city is at the centre of the epidemic in Britain, said people must obey the guidance or others would die.

"This isn't advice, as far as I'm concerned. These are instructions and these are rules that we should all obey to stop people dying," he told BBC1's The Andrew Marr Show.

Scotland's First Minister Nicola Sturgeon announced she was closing the ferries to the Scottish islands to all non-essential travellers after the military was brought in to transport a patient to the mainland.

She said people should not go shopping "except for essentials like food and medicine" and she condemned people "flocking" to Scotland's remote communities for adding to the pressure on local health services.

"Beaches should not be busy, parks should not be full," she said.

Mr Johnson said the "shielding" of the 1.5 million people considered to be the most vulnerable to the coronavirus - requiring them to stay at home for 12 weeks - would do "more than any other single measure to save life".

They include people with severe respiratory conditions and those suffering from some cancers such as those of the blood or marrow.

Communities Secretary Robert Jenrick said that, with the help of military planners, the Government was creating a network of local "hubs" to ensure those without family or friends to support them received their medicines and other vital supplies.

"Nobody needs to worry about getting the food and essential items that they will need," he said.