Britain's Business Secretary Kwasi Kwarteng said he was concerned by a so called 'pingdemic' in which hundreds of thousands of workers have been told to self-isolate after being alerted by the NHS Covid app as fears grew of food and fuel shortages.

"We're very concerned about the situation," Mr Kwarteng said when asked about reports of empty supermarket shelves in some areas. "We're monitoring the situation."

Britain's food supply chains are "right on the edge of failing" as absence related to Covid-19 has aggravated a critical shortage of labour, a meat industry body said yesterday.

Almost 620,000 people in England and Wales were told to isolate by the NHS app after they came into contact with someone with the virus in the week up to 14 July, official data shows.

The data showed that 618,903 people had received an alert from the contact tracing app.

According to the data, 607,486 alerts were sent to people in England.

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Mr Kwarteng said a list of critical workers who will be eligible for loosened isolation rules if pinged by the NHS Covid app will be drawn up "very soon".

No 10 has previously said "we're not going to be producing a list covering individual sectors".

Speaking on Sky News, he said: "We're going to announce a list of exempt workers. The list of exemptions will be quite narrow because, obviously, you have to draw the line somewhere."

Mr Kwarteng would not say who would be on the list or say whether it would come this week, but insisted it would be "very soon".

A food distribution firm struggling with staff shortages is advising workers who are pinged by the NHS app to take tests and continue working, in breach of government advice.

Bidfood chief executive Andrew Selley defended his approach for delivery drivers to continue working if they have negative results as "appropriate and safe" because they are "critical workers".

He said the firm, whose customers include hospitals, has heard no information about how to apply for an exemption for some fully-vaccinated staff to avoid quarantine under new plans to ease the "pingdemic".

Amid a "real challenge" in completing orders on time, he said workers are being asked to follow a testing regime if they receive an alert from the app as a close contact.

"If they are pinged we ask them to take a PCR test, if that's positive then clearly they'll isolate, but if it's negative we ask them to come back to work and we have a process of doing lateral flow tests daily away from their workplace, and if that's negative they can proceed with their work."

Official advice from the UK government is to isolate for 10 days after an alert from the app, but it is not a legal obligation like if contacted by Test and Trace.

Mr Selley said 100 staff from around 20 depots across the country were off isolating yesterday, presenting a "real challenge" with deliveries delivered late, or even the next day.

Prime Minister Boris Johnson has announced an exemption for a "very small number of named critical workers" who have received both jabs, ahead of a greater easing of the rules for the fully-vaccinated on 16 August.

But he has faced pressure to go further as businesses struggle with shortages as coronavirus cases soar.

This week business minister Paul Scully said it was a decision for individuals and employers whether they should isolate after a "ping" from the app.

But he was quickly contradicted by Downing Street, who insisted it is "crucial" for people to self-isolate after receiving an alert from the NHS Covid-19 app.

Additional reporting PA