Britons have been ordered to stay in their homes as the fight against coronavirus is ramped up, with all non-food shops forced to close and police handed powers to fine anyone in breach of the lockdown.

In an unprecedented address to the nation last night, Prime Minister Boris Johnson warned the country faced a “moment of national emergency”.

Speaking shortly after Mr Johnson, First Minister Nicola Sturgeon said the measures “amount to what has been described as a lockdown”.

It came amid anger at images of overcrowded trains and parks just days after pubs, restaurants and leisure venues were shut down in a bid to enforce social distancing measures.

In measures which finally bring the UK into step with much of the continent, including Italy and Spain, householders are banned from going out except to shop for basic necessities such as food and medicine, and should do so “as infrequently as possible”.

Home delivery services should be used instead, if possible.

Travel to and from work is permitted only if it is “absolutely necessary and cannot be done from home”.

People will be allowed to take exercise such as a walk, run or cycle once a day, but only with members of their own household.

Meeting up with friends or family members you do not live with is forbidden. Shops not selling food or medicine must close, with libraries, playgrounds, outdoor gyms and places of worship also shut down.

Weddings, baptisms and other celebrations could be subject to police fines. Parks will remain open but groups of people will be dispersed.

Both the UK and Scottish governments plan to publish emergency legislation in the coming days to give police powers to enforce the new rules. “We will stop all gatherings of more than two people in public – excluding people you live with,” said Mr Johnson.

He added: “Everyone from the supermarket staff to the transport workers to the carers to the nurses and doctors on the frontline. But in this fight we can be in no doubt that each and every one of us is directly enlisted.

“Each and every one of us is now obliged to join together. To halt the spread of this disease. “To protect our NHS and to save many, many thousands of lives. And I know that as they have in the past so many times.

“The people of this country will rise to that challenge.”

Chief Medical Officer Dr Catherine Calderwood said enforcement action would only be necessary if people do not take the restrictions seriously.

She said the more people comply, the less impact there will be on the NHS and the more lives can be saved. “I stress again, this is not a rehearsal,” she said.

“This is real life. And lives will be lost unless everyone changes what they’re doing from now on.”

It came as the UK death toll from Covid-19 rose to 335, with four new deaths in Scotland and 23 coronavirus patients currently in intensive care north of the Border.

Hours earlier, First Minister Nicola Sturgeon said that hair salons, building sites and all non-essential food shops should close to help slow the “rapid acceleration” of cases.

Ms Sturgeon warned that pubs which had ignored instructions to shut at the weekend would be forced to close as soon as emergency legislation is passed this week.

She added: “My message to shops that remain open is this: if you are not providing essential items such as food and medicines then please close now.

“However, it has become clear to me that there are still far too many people expected or expecting to go into work as normal, and that presents a serious and unnecessary risk of transmitting the virus.

“So I want to reiterate that if you run a business and the nature of your business makes it difficult for you or your workers to practise social distancing then you should close for the period of efforts to combat this virus.”

Retailers including John Lewis and Primark have already closed, and fastfood giant McDonald’s closed all its outlets in UK and Ireland last night saying it had become “increasingly difficult” to maintain safe social distancing while continuing to operate as a takeaway and drive-thru service.

Greggs will also close all its UK branches today. Ms Sturgeon added that her advice to building sites and hair salons in particular “would be to close”.

“These measures are not easy but they are necessary,” said the First Minister.

“They are necessary for us to slow down what is becoming a rapid acceleration of this virus.”

Over the weekend, photos emerged showing crowds of people visiting open spaces across many parts of the UK. Emyr Williams, chief executive of the Snowdonia National Park Authority in Wales, said Sunday had been the park’s “busiest visitor day in living memory”.

On Monday images also emerged of ScotRail and London Tube trains packed with morning commuters.

It came as public transport operators across the UK introduced reduced timetables, with ScotRail responding to customer complaints on Twitter by stressing that it was also experiencing staff shortages due to a number of employees being in self-isolation.

Finn Brenna, Aslef organiser, said only key workers such as NHS and supermarket staff should still be commuting.

“We need the Government to shut down all non-essential work,” he said.

It comes amid warnings that the virus was leaving previously healthy young people fighting for their lives.

In the West Midlands, 36-year-old nurse and mother-of-three Areema Nasreen is on a ventilator in intensive care after contracting coronavirus. Her family said she had previously been “fit and healthy”.

Labour MP Rosena Allin-Khan, who also works as an A&E doctor in London, said her latest shift had been a “ deeply eye-opening” experience with previously fit and healthy people in their 30s and 40s “attached to machines, fighting for their lives”.

In Hong Kong, tourists will be banned from entering for 14 days from tomorrow. It comes as it battles a so-called ‘second wave’ of infections.

The territory had appeared to be a blueprint for containment, after reporting relatively few cases at the height of China’s outbreak as a result of virus mapping, social distancing, intensive hand-washing, and use of protective gear by medics.

However, in what is seen as the danger to countries of letting their guard down too soon, the number of confirmed cases of Covid-19 in Hong Kong almost doubled in the past week.