Police forces are stepping up patrols and road checks to prevent people flocking to beauty spots over the Easter weekend.
Officers fear that the warm and sunny weather forecast for much of the UK over Good Friday and Saturday will tempt people out of cities into the countryside.
With the current coronavirus lockdown likely to be extended, the National Police Chiefs’ Council (NPCC) warned that officers “may have to ask people about their circumstances if they’re outdoors”.
“During this long weekend, please help the NHS and those most vulnerable in our communities by staying home unless your journey is essential – even when good weather or sheer frustration could tempt us outside,” said its chair, Martin Hewitt.
“We will engage with the public, explain the social distancing regulations and the responsibilities we all share, and encourage those who are out without good reason to go back home.
“Where people don’t comply, we will direct them to go home, and if necessary we will issue a fine.”
British Transport Police, which wrongfully prosecuted a woman under the Coronavirus Act last week, said officers would patrol railway stations popular with daytrippers.
Superintendent Glen Alderson said: “Only those making essential journeys should be using the rail network.”
Assistant Chief Constable Glen Mayhew said: “Essential travel does not include visits to second homes, camp sites, caravan parks or similar, whether for isolation purposes or holidays.”
Cumbria Police issued a frank message on social media, saying: “If you are thinking of coming to the Lakes this weekend for a holiday – don’t.”
The Lake District is among areas where the owners of Airbnbs and holiday homes are accused of continuing to allow visitors.
Chief Constable Michelle Skeer said: “This is not a time for tourists to be travelling to the county. My officers will be on patrol, in all areas across the county, particularly in popular areas and gathering spots.”
She said people travelling into the county or ignoring social distancing guidelines could be fined and arrested.
Hampshire Police cautioned people against “taking advantage of the expected upturn in weather and visit green spaces, beaches and national parks”.
“We may need to ask you about your circumstances if we see you out and about or travelling so please continue to consider if your journey is essential,” said Assistant Chief Constable Scott Chilton.
The Traffic Wales authority said police were patrolling the country’s entire road network and “if your journey is not deemed essential then you will be told to return to your home address and may be fined”.
North Wales Police said officers had spoken to people “travelling miles for a ride in the car or to go kite surfing on the beach”.
Temporary Assistant Chief Constable Nigel Harrison added: “Our advice is do not travel into north Wales illegally. Moving around can easily accelerate the spread of the virus.”
Gwent Police said officers would be “carrying out enhanced patrols” over Easter, “engaging with motorists and questioning behaviour that does not follow government guidance”.
Police Scotland have appealed for people not to flock to the Highlands and ferry operator Caledonian MacBrayne, which runs services to the Hebrides and other islands said people on non-essential journeys “will not be allowed to travel”.
Director of operations Robert Morrison added: “Only essential travellers are currently being allowed to board which includes food and medical supplies, utilities workers, transport and the emergency services.”
Northamptonshire Police Chief Constable Nick Adderley said that if people continued to flout restrictions, his officers would set up roadblocks and could even start searching people’s shopping trolleys.
Speaking at a press conference on Thursday, he added: “If things don’t improve, and we don’t get the compliance we would expect, then the next stage will be road blocks and it will be stopping people to ask why they are going, where they’re going.”
The warnings came after police forces across the UK introduced dedicated online tools for people to report alleged lockdown breaches.
Officers are encouraging people to use the forms rather than dialling 101, which was inundated with calls after the restrictions were announced.
Cambridgeshire Constabulary said it would not be dispatching officers for “minor infringements” but would respond to mass gatherings.
Police have been given the power to arrest and fine people for breaking the new Health Protection Regulations, although leaders say officers must only use enforcement as a “last resort” after encouraging people to comply voluntarily.
The standard penalty is £60, reduced to £30 if paid promptly, but the amount can be increased for repeat offences up to £960.