The news comes as people were spotted sunbathing on Saturday the hottest weekend in the past six months – which is the second the UK has locked out due to Covid-19.
Speaking at the daily Downing Street press conference, Cabinet Secretary Michael Gove said there is “evidence to suggest” that compliance varies with different demographics of the population.
“This is why it is important to reach them appropriately – some of the messages and some of the channels we have used may not have reached certain segments of the population.
“Young people may feel they are less likely to be affected and less likely to be infected.”
Images posted on Twitter showed crowds of people at London Fields and Battersea Park in the capital, some having been tanned and others renting bikes.
In the northeast, surfers were photographed on Tynemouth Beach.
Jody Richardson, 43, said he “saw 25-30 people in the area” and “very little or no social distancing” when he went for a walk with his partner and children at Orwell Country Park this afternoon.
He told the Palestinian Authority news agency: “We were so disgusted that it was happening in our area that we stopped our walk with our children and our dog and went back and went home.
He added, “There was very little room on the paths to be able to safely avoid people and leave the two meter gap. “
Gove urged people to heed the current pressure on the NHS and ask themselves, “How can I help in this shared national effort?”
He added, “I know that locking is difficult, I know that it is very difficult, especially for families with children.
“But people have to follow these guidelines every step of the way because that is the only way to make sure that we limit the spread of the disease.” “
One crowded place was Brockwell Park in south London, which will now be closed on Sunday because many flout government advice on social distancing, said the Lambeth Council.
He tweeted, “Despite clear advice, over 3000 people have passed through Brockwell Park today, many of them sunbathing or in large groups. This is unacceptable. Unfortunately, the actions of a minority mean that, following advice from the police, Brockwell Park will be closed tomorrow. #Stay at home “
The board added, “We are sorry we had to make this decision. This should not happen if people followed clear government instructions. We do this for the safety of the public. A minority of people did not follow the instructions – unfortunately, we have to act. “
Calls to respect the lockout were made nationwide, and the Bournemouth Pier was adorned with the message “Stay at home” – with only a few people seen walking along the most desert sands on Saturday.
There were also sparse scenes in Canon Hill Park in Birmingham, where a few people were pictured running.
Gloucestershire police said the police would arrest those who appeared to be walking away for a few days.
The force said, “There has been particular concern in some communities that people with second homes in the area are visiting during the Easter holidays,” and they may put additional pressure on the local NHS.
Wales authorities have closed beachside parking lots to dissuade people from “using the weather to treat what is a national crisis as a national holiday”.
The Dorset Council took the same approach, and the council closed the waterfront parking bays and stopped the RNLI patrol in an effort to prevent people from gathering by the sea.
Met Office meteorologist Steven Keates said Sunday will be “a beautiful spring day” with “blue skies and sunshine for much of the day for much of the UK”.
He predicted that parts of the UK “could see 20-21C”, which would be “the first time we have reached more than 20 since October 1 of last year”.
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