Pubs that flout government instructions to close during the coronavirus pandemic risk losing their licences, a police chief has warned.
Lancashire Police said it had been told of pubs holding "lock-ins" despite the government announcing on Friday that licensed premises should shut.
Derbyshire and South Yorkshire police have received similar reports.
Lancashire Police's Deputy Chief Constable Terry Woods said "this has got to stop".
"If you carry on then [you can] expect significant problems obtaining a licence when the time comes to open."
He told BBC Radio Lancashire the force had received a "few" reports of pubs breaching the order.
"Any police action we take subsequently is about saving life. These rules are here now and it's not a request, it's a government order," he said.
Derbyshire Constabulary also received a "large number of reports" that pubs opened at the weekend, a force spokesman confirmed.
"Any licensee who fails to comply with the government regulations and the terms of their licence may be handed prohibition notices and potentially unlimited fines," the spokesman added.
"They may also face the loss of their alcohol licence."
South Yorkshire Police is contacting all licensed premises to make sure they understand the new requirements after a minority remained open at the weekend.
Asad Khan, a consultant respiratory physician at Wythenshawe Hospital, Manchester, said it was "completely unacceptable and dangerous" that some people were ignoring government rules.
"The public are somehow under the impression this is a mild illness unless you are frail, elderly or have other medical conditions," said Dr Khan.
"It's true that the elderly have higher death rate, but it doesn't mean young people aren't affected in a significant manner."