It will be "nigh-on impossible" to enforce the government's plan to require the wearing of face masks in shops, police officers have said.
Ken Marsh, chair of Metropolitan Police Federation, said forces should not be charged with overseeing more pandemic rules and that shopkeepers needed to "take some responsibility" for their customers.
"If a shopkeeper calls the police because someone's not got a mask on they have no power to detain them so that person can just walk away. We'll be driving round and round London looking for people who weren't wearing masks, it's absolutely absurd," he said on Tuesday morning.
But some retailers have expressed discomfort at the idea that shop workers could be made to confront shoppers not wearing masks, with a new rule set to come in in England from 24 July.
"I think it's our intention to offer a face mask to those people who are not wearing one. Of course, if they refuse to wear one I think the actual enforcement is not for the store colleagues," said Peter Cowgill, chairman of national clothing chain JD sports.
"I think it's a very difficult situation and I'm surprised by the inconsistencies of the messaging. I'm not sure that it applies to bars or restaurants, there's obviously been a long period where supermarkets have had throngs on people."
James Daunt, boss of bookseller Barnes and Noble said on Monday ahead of the announcement: "I definitely do not think shop workers should be the police of it – that would not be right. Because there are a tiny, tiny minority of people who will be confrontational over it and it is not the position of shop workers to enter into that situation."
JD Sports' Mr Cowgill told BBC Radio 4's Today programme that the government's "inconsistencies and the indecisiveness" in announcing the policy "at the back end of the pandemic" made the situation more difficult and that many customers could be put off from shopping.
On Sunday Boris Johnson's deputy Michael Gove said emphatically that masks would not be made mandatory, but on Monday night the government announced that they in fact would be – but with a 10 day delay.
Ministers were telling the public not to wear masks as recently as April, claiming they were ineffective and could create shortages for health workers – leaving Britain as an international outlier with low mask uptake. The latest evidence suggests they are effective at stopping the spread of Covid-19.
Mr Cowgill added: "It's come as a surprise, the lateness, a bit like quarantine – it seems to have come at the back end rather than the front end of the pandemic. And it's been delayed until July 24 which is very difficult to work out and seems quite indecisive." He added that he was "not sure about the rationale for the delay".
120 countries around the world either require or strongly recommend the wearing of masks in enclosed public space. But how such a rule will be enforced in Britain remain to be seen. The Met police federation's Mr Marsh told the BBC: "This cannot all be laid on the shoulders of the police yet again.
It will be nigh on impossible for enforcement
Ken Marsh, Met Police Federation chair
"It will be nigh on impossible for enforcement because you won't have a police officer on every shop door because there isn't enough of it.
He added: "It's more than a difficult position, it becomes a position where it is them and us yet again. We've seen this throughout this Covid pandemic - it has always become the police's problem to deal with this."
George Eustice, the Environment Secretary said there was a role to play for both the police and retailers but that ultimately only police could issue fines.
"With all of our laws there is an element of policing by consent and so we need the public to play their part and to abide by these restrictions," he said.
"In some ways this isn't new – we've had to do some pretty extraordinary things throughout this coronavirus pandemic."
He added: "I think when it comes to levying fines and actually having that sanctions and issuing a fixed penalty notice of £100 then obviously the police do have to do that.
"But then there's a separate question which is will retailers play a part in this and I think obviously they will ... they will have a role to play in helping ensure there's compliance. They may in some cases hand masks out to people if they don't have one, I'm sure that they will tell people that they should be wearing one, but if it comes to that final sanction of issuing a penalty then that's something only the police can do."
Mr Eustice also defended accusation that the government had botched the policy with mixed messages and late introduction.
"I think if you go right back to May we gave guidance at that point that people should wear a mask when in enclosed spaces ... I don't think it's very bothered about who said what when," he said.