Companies in "critical" industries will have to apply to the Government if they want key workers to avoid self-isolation when pinged by the NHS app, it was confirmed on Thursday.
The Government has named the sectors that can benefit from an exemption to the normal rules for people to quarantine for 10 days if they come into contact with someone who tests positive for Covid.
The list includes energy, telecoms, food production and supply, waste, water, essential transport, emergency services, border control and medicines.
However, most organisations in those sectors will not be able to apply for a blanket exemption for staff, as industry leaders had wanted.
Employers have to prove they face "major detrimental impact" to business to be eligible for the scheme. But the guidance makes it clear that "not all or in most cases even the majority of workers in critical sectors" will be covered by the scheme.
Only companies that have received a letter from the Government approving their involvement will be able to to let "named" workers avoid self-isolation.
Instead, they can petition the Government to allow a number of employees to continue working despite having been told to self-isolate – with no guarantee of success.
It raised questions about how quickly approvals could be turned around and how easy it would be to get the green light to take part in the scheme.
The exemption, announced earlier this week, is designed only to apply to a "very small" number of workers "critical" to the national infrastructure.
Downing Street also moved to better protect food supplies by vowing to create up to 500 testing sites to ensure that employees in places such as food distribution centres can keep working. Companies in food production will be able to apply for exemptions from self-isolation for groups of staff rather than on an individual basis.
More than 600,000 people were pinged in the week leading to July 14, it was announced on Thursday, with figures suggesting more than one million in total are self-isolating when the numbers contacted by NHS Test and Trace are included.
Over half a million 'pinged' at start of July
Business leaders fear the numbers could soar even higher, with close to 50,000 new Covid cases being registered in the UK every day.
The rules are due to change on August 16, when people who have been double jabbed can take daily Covid tests rather than self-isolate if pinged – but calls for that to be brought forward are growing.
Two former Tory health secretaries, Jeremy Hunt and Lord Lansley, called for people who are pinged to be able to take a negative test and return to work in an attempt to ease pressure on the economy.
Lord Lansley, who was Health Secretary from 2012 to 2014, told The Telegraph: "I think if those pinged then get a negative PCR [result], it should be regarded as a ‘test to release’ and this will be an option for employers to reduce the negative impacts on them."