Food supply chains are “starting to fail” because of workers isolating over coronavirus contacts, an industry leader has warned, as he criticised Boris Johnson’s effort to ease the “pingdemic”.

A meat industry trade body said it cannot rely on the Prime Minister’s new exemption for some fully-vaccinated critical workers because the bar has been set “very, very high”.

Mr Johnson apologised to businesses for the “inconvenience” on Wednesday but told them to stick with isolation rules after confusion was sown by his own ministers.

In the face of widespread criticism over staff shortages as Covid-19 cases soar, the Prime Minister this week announced a plan for a “small number” of critical workers to be able to continue their functions.

There’s an air of despondency creeping through the industry

But British Meat Processors Association chief executive Nick Allen criticised “confusing messages” from the Government as he said ministers have not clarified who is applicable.

“There’s an air of despondency creeping through the industry really. Until now we’ve managed to keep the food supply chain running but there’s a sense of, we’re starting to fail on that front,” he told BBC Radio 4’s Today programme.

Asked if production lines are stalling, he said: “They are. It’s happening already. We’re starting to see that at retail level and in restaurants – everyone is struggling to get things out really.”

He said the industry is not clear who is covered by the exemption for a small number of double-jabbed critical workers.

“It was made very clear to us late yesterday that this exemption will be for very, very few people. They described it as setting the bar very, very high and we’re certainly not counting on that,” he said.

Pubs and shops have complained about having to close because of the the number of people being “pinged” as contacts by the NHS Covid-19 app, while medics have also raised concerns.

The latest figures show more than 500,000 people in England and Wales were asked to isolate by the NHS app in the week up to July 1.

Mr Johnson urged people to stick with the rules until they change because “isolation is a vital tool of our defence” during a Prime Minister’s Questions in which he appeared virtually from his own quarantine in his Chequers country residence.

“I apologise to everybody in business up and down the land in all kinds of services, public sector or otherwise, who are experiencing inconvenience,” he added.

Sir Keir Starmer accused Mr Johnson of “trying to dodge” his own quarantine after his contact with Covid-positive Health Secretary Sajid Javid and highlighted inconsistencies in policy.

“When it comes to creating confusion the Prime Minister is a superspreader,” the Labour leader said, as he accused Mr Johnson of ushering in a “summer of chaos”.

On Monday, Mr Johnson resisted calls from businesses struggling to cope with reduced staffing levels by declining to introduce a more wide-reaching change to quarantine rules ahead of August 16, when a testing regime will replace the requirement for fully-vaccinated contacts to isolate.

He has suggested an exemption would cover some in hospitals and care homes, or working in the supply of food, electricity and medicines, and transport, defence and borders.

But the Government has said there is no “blanket exemption for any sector or role” and decisions will be made largely on a case-by-case basis.

Downing Street has declined to say how many people will be granted exemptions, but it is understood the figure is not expected to reach the high tens of thousands.

No 10 was this week forced to stress that quarantining after an alert from the app is “crucial” after business minister Paul Scully suggested people could make an “informed decision” on whether to quarantine.