Police face “one of their biggest challenges” of the lockdown this weekend as sunny weather risks drawing crowds to parks and beauty spots.
Katie Bourne, Sussex Police and Crime Commissioner, told the BBC officers were telling the public to “hang on in there” and avoid unnecessary trips.
Ministers have said “stay at home” is an instruction, not a request.
And senior medics urged people to avoid travel for the sake of two nurses who died of coronavirus.
A forecast of warm weather in some areas this weekend has led to warnings from local councils, tourism bosses and police urging people to stay away from coastal areas, national parks and other visitor destinations.
On Sunday, forecasters have predicted a temperature high of 20C in south-east England, while southern Scotland and the Midlands could reach 16C and 19C respectively.
“This weekend is going to be one of the biggest challenges for policing so far,” Ms Bourne told BBC Newsnight.
“We’ve been through a lot, it’s very disruptive but let’s not give up, let’s hang on in there. It’s a collective endeavour, this is ultimately about saving lives and not putting a strain on the NHS and our other emergency services.”
It comes as the latest figures showed 3,605 people with the virus have died in the UK, with 684 deaths recorded on Friday. There are 38,168 confirmed cases.
Health Secretary Matt Hancock said at the No 10 briefing on Friday: “We cannot relax our discipline now. If we do, people will die.”
Mr Hancock said the advice to stay home and protect lives is “not a request – it is an instruction”.
After the deaths of two nurses with the virus, Areema Nasreen and Aimee O’Rourke, England’s chief nursing officer Ruth May said: “Please stay at home for them.”
Lord Kerslake, the former head of the civil service, told Newsnight the UK was at “a critical moment” for maintaining the lockdown but said it had to be done through “90% persuasion and 10% enforcement”.
Focusing the messaging on the weekend weather risked “trivialising” the sacrifices people were making, said Lord Kerslake.
“People’s lives are hugely disrupted, they are separated from their loved ones, their jobs are at risk and we have to be empathetic to their circumstances and at the same time very clear about the need to stay home,” he said.
Test shortages
Also this weekend, the Queen is due to make a rare special address to the nation on TV, radio and social media.
The speech at 20:00 BST on Sunday will be intended to reassure and rally people, BBC royal correspondent Nicholas Witchell said. The Queen is also expected to thank NHS staff and key workers, as well as emphasise the important role individuals can play.
The decision to deliver the speech has been made “in close consultation with Downing Street”, he added.
Meanwhile, the body representing laboratory scientists said the government’s plans for scaling up testing for coronavirus infections to 100,000 a day risked being held up by a shortage of chemicals and supplies.
The Institute for Biomedical Sciences said the UK had enough laboratories and staff to increase testing, but there is a “very real risk” that hospitals could run out of reagents, the chemicals used in the tests.
And supplies of the the precision plastics used with the reagents are not due to be ready until mid-May, the institute said.
