Ministers have ruled out extending the list of workers who are exempt from self-isolation rules and warned that the August 16 date for lifting quarantine for double-vaccinated people could be delayed.

George Eustice, the environment secretary, said he recognised the “stress” that staff shortages were causing for businesses after a record 618,903 people were pinged by the NHS Covid-19 tracing app last week.

However, he defended the government’s decision to limit the lifting of self-isolation requirements to food supply workers, saying ministers were keeping “a very close eye” on the number of hospital admissions.

He also suggested that the government could delay the August 16th date when all self-isolation rules are lifted for double-vaccinated people, saying the government had only announced the date to give people “some kind of indication” of when rules might change. He warned that the date could still move “in either direction”.

Supermarket depot workers and food suppliers will no longer have to self-isolate for ten days if they come into contact with a positive case and will be able to take daily tests instead. The government has also published a list of 16 industries where businesses can apply for an exemption from self-isolation if a worker is pinged by the app.

However, businesses have said the relaxation of measures do not go far enough and have called for the August 16 deadline to be brought forward.

Rail workers warned commuters to expect line closures next week because of staff shortages. Port operators said they were baffled why they had not been included in the same category as supermarket depot workers and food manufacturers.

Tim Morris, chief executive of the UK Major Ports Group, said: “Employers now need to go through a laborious process of producing, agreeing and receiving official letters of approval from the government of named individuals. However, it seems that thousands of supermarket staff get waved through without any such process. We simply don’t understand why it’s one rule for one sector and another for the critical pinch points in the economy.”

Eustice was asked this morning if the exemption list would be expanded to include workers from other sectors beside the food supply industry.

He told Sky News: “The reason we’ve made a special exception for food is for very obvious reasons — we need to make sure that we maintain our food supply.”

“When it comes to other sectors, yes, of course the fact that they are also carrying high absence levels is causing some stress for them and making it more difficult.”

“You also have to bear in mind why we’re doing this and we are trying to still just dampen the pace and the velocity at which this infection is spreading because we have to keep a very close eye on those hospitalisations.”

The minister was also asked why the government had announced a firm date of August 16 for lifting self-isolation rules rather than ease measures closer to the time on the basis of infection data.

He said: “I think people want to have a clear idea of where they stand. The reason we have set that date — of course, things could always change in either direction — but the reason we set these dates is to give people some kind of indication of what they can expect.”

Within the food supply industry, there was still confusion this morning about what workers would be exempt.

Richard Harrow, chief executive of the British Frozen Food Federation, said the exemption list was “worse than useless”.

Nick Allen, chief executive of the British Meat Processing Association, said: “We’ve been told there will be more detail coming out on Monday, which I think is disappointing. We’re delighted that the government has recognised there was a problem bordering on a crisis and something needed to be done but there needs to be recognition this is a 24/7 supply chain, and you can’t wait to Monday to understand who’s going to get this and how it’s going to work — I’ve been inundated with questions from members about how it’s going to work that I just can’t answer at the moment.”

Supermarket staff and suppliers will be exempt from quarantine if they have been fully vaccinated.

Workers in 2,000 warehouses and supermarket distribution centres who are identified as contacts of people with covid will be allowed to take daily tests at work instead of self-isolating.

It represents a significant retreat by the government after Boris Johnson said only a “very small” number of people would be allowed to use testing to avoid quarantine. Up to 10,000 staff are expected to qualify for the scheme.

John Foster, CBI Director of Policy, said: “The exemption list will help some of our critical sectors to keep moving but it will rapidly become significantly challenged. First, the idea of potentially thousands of businesses emailing Whitehall officials to request approval for individuals to go to work is undeliverable let alone undesirable. Second, the list is slim, missing out many businesses in the supply chains that will be crucial to the running of these key industries so will need to be significantly expanded within days.

“We welcomed the Government’s strategy to open the economy and support a new approach to living with the virus and noted they believed now was the right time to make headway on that strategy before the Winter.

“If we want the economy to stay open, we need a confident but balanced plan. We should bring forward the date from 16 August when those who have been double-jabbed no longer need to self-isolate if they test negative once contacted. We also need a test & release scheme for those who have not been double jabbed. And we should use testing and Covid safety measures to promote a culture of safety and mutuality in workplaces, shops, hospitality and public transport.

“We need mass testing – not mass self-isolation – to tackle staff shortages. That’s why the government should be applauded for moving to a test and release scheme for the food industry to help relieve staff shortages. This is exactly the kind of agile response that firms need to build confidence in the reopening. If the Daily Contact Testing scheme is deemed as a good, safe solution by the government, the next step must be to scale this up at pace. This scheme illustrates what it is to live with the virus.

“More broadly, it’s critical to have the right balanced plan not just for the next few weeks but also for the next 12 months as we consider how a well vaccinated population deal with difficult evolutions of the pandemic.”