Downing Street has warned England could be plunged into another lockdown if Brits continue to cram onto beaches during the heatwave.
Shocking scenes of a heaving Bournemouth Beach prompted Dorset authorities to declare a major incident on Thursday.
Thousands travelled to the coast and packed out the beach, flouting social distancing guidelines as they squeezed together in the 33C temperatures.
The overcrowded beaches caused chaos along England's coastline - despite authorities pleas to stay away as the UK's official coronavirus death toll tops 43,000.
Downing Street reminded the public that if breaching of social distancing goes on, the lockdown could be ramped up again.
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Asked about the beach scenes at Thursday lunchtime, Boris Johnson's official spokesman said: “It's not for me to pass comment on particular photographs.
"What I would say is that the PM and the government's scientific and medical advisers have stressed the great importance of the public continuing to adhere to social distancing advice.
"It's only because of the public's hard work that we've been able to bring the virus under control.
“If the rules don’t continue to be followed and the virus starts to spread exponentially again, then we will look at having to reverse some of the easements that we’ve put into place.
"And I don't think anyone in the British public would want for that to happen."
Environment Secretary George Eustice warned there is “clearly an increased risk” for people packing Bournemouth Beach and it was of "concern".
He told BBC Breakfast: “I’ve seen the pictures of Bournemouth and yes, obviously, looking at the crowds of people there, there’s clearly an increased risk when you have such large numbers of people.
“The scientific advice is in outdoor environments the risk of transmission is much lower, but even in an outdoor environment if you’re within two metres of somebody else for a period of 15 minutes or more there is some risk.”
Mr Eustice echoed warnings that beaches could be closed - or even the opening of pubs and restaurants from July 4 reversed - if rules are broken.
He said the next stage of opening restaurants and pubs “would be the most difficult, and we’d only be able to do that and keep the virus under control if people observe social distancing.”
And he warned there was a "quid pro quo" where they would only reopen if the public follow distancing rules.
Asked if beaches could be shut, he said: “We do have powers to put in place closures should that be necessary but we don’t really want to go to that.
“If it were necessary to do that to control the virus then of course we would. And Matt Hancock made that clear yesterday.”
But he also suggested beaches would only shut if they were rammed "day after day after day" - and claimed things “will return to normal” after the “abnormally” large crowds on a hot day.
The minister added: "We just have to recognise yesterday was the hottest day of the year, incredibly hot, a lot of people had the same idea, they all went to the beach, and yes of course those scenes at Bournemouth are a matter for concern.
"The British weather being what it is maybe that will be short lived and people will return to the type of social distancing they've actually demonstrated quite well."
Hordes of beach-goers left Bournemouth locals disgusted as they clogged up traffic, squeezed on and off trains meant for essential travel only, and boozed on the beach.
Police were forced to attempt to disperse the huge crowds yesterday, as beachgoers ignored authorities' pleas to stay away.
The sunbathers left mountains of litter behind, with the council removing tonnes of rubbish off the sands throughout the day.
The 'stretched' local police were pleading with people to stay away, and the council raged at tourists gridlocking roads, dumping rubbish and parking illegally.
Three beaches were under major pressure yesterday amid the hottest day of the year yet.
An incident had to be declared at Formby Beach in Merseyside too, where police were called-in to break up large crowds.
And an order was in place in Orcombe Point in Exmouth, Devon too on Thursday, after up to 200 people were involved in a mass brawl in front of horrified families.
Health Secretary Matt Hancock threatened last night to use government powers to close beaches.
Mr Hancock told TalkRadio the Government had the power to close public areas such as beaches if people flout safety restrictions.
Downing Street later rowed back on his comments.
A No10 spokesman said: "I believe Matt Hancock, when he spoke, was referring to the powers to impose localised lockdowns.
"We have been clear throughout [they] may need to be the case if we see case numbers rise in a particular area."
When it comes to directly shutting beaches, he added: "Local authorities are best-placed to make these decisions on a case-by-case basis."
Chief medical officer for England Professor Chris Whitty issued a direct warning to Brits of a potential for a second wave of deadly Covid-19.
He wrote on Twitter yesterday: "Covid-19 has gone down due to the efforts of everyone but is still in general circulation.
"If we do not follow social distancing guidance then cases will rise again.
"Naturally people will want to enjoy the sun but we need to do so in a way that is safe for all."
The warning klaxons from the leaders come barely a week before measures are due to ease again, including a new "one-metre plus" social distancing rule.
Businesses including pubs and hairdressers are set to reopen from July 4 and socially distant socialising between households indoors will be permitted.
Bournemouth Council leader Vikki Slade said yesterday she was "appalled" at the behaviour on the beaches.
She cited "the irresponsible behaviour and actions of so many people" and declared a major incident.
"[It] is just shocking and our services are stretched to the absolute hilt trying to keep everyone safe," she said.
The council leader slammed the irresponsible sun-seekers.
She said: "The numbers of people descending down here are like those seen on a bank holiday.
"We are not in a position to welcome visitors in these numbers now or to deal with the full range of problems associated with managing volumes of people like this.
"Please do not come. We are not able to welcome you yet.”
