People in frontline roles such as police, fire and the Border Force, will be able to avoid quarantine - regardless of vaccine status - if they are a close contact of a positive COVID case, as the government expands workplace testing in England.
Emergency service workers and other critical staff, including those in transport, freight and haulage, were already eligible to be exempt from self-isolation - but only if their employers specified their names and that they were double jabbed.
Now they will be able to take part in the scheme whether they are vaccinated or not, as new testing sites will be established.
An expected initial extra 200 test sites are set to be opened, meaning daily contact testing could be "rolled out to further critical workplaces in England", said the government.
But they are not expected to be operation until Monday at the earliest.
The expansion came after the government on Thursday announced its programme would allow around 10,000 workers at up to 500 sites in the food sector to avoid the need to self-isolate for 10 days if identified as a contact of a coronavirus case, and instead take daily COVID tests.
It is understood the workers also don't have to be inoculated to be part of the scheme.
From 16 August, all people in England who are double jabbed will be exempt from self-isolation if identified as a close contact.
But Boris Johnson is facing growing pressure to allow more of those fully vaccinated to be exempt soon.
London Mayor Sadiq Khan has joined business leaders in calling for further workers to be allowed to skip quarantine if they are alerted by the NHS COVID-19 app to prevent a staffing crisis during the so-called "pingdemic".
In a letter to the prime minister, the mayor and industry bodies including UKHospitality, the London Chamber of Commerce and Industry and London's branch of the Federation of Small Businesses, said there is "an urgent need to outline a more considered approach" on the rules regarding self-isolation.
They warned that the app is exacerbating staff shortages for pubs, bars and restaurants.
The government has announced that a phased approach to testing will soon see some "critical workers" being exempt from quarantine as long as they use daily lateral flow tests and the results are negative.
But the mayor and business leaders said daily PCR tests should be used instead.
"The summer months are crucial for many businesses' recovery and their ability to recover must not be put in jeopardy," they noted.
"We are therefore calling on you to ensure that the necessary testing is in place to enable people who have been double vaccinated for longer than two weeks and pinged by the NHS COVID app, to immediately return to work, following a negative PCR test, rather than having to self-isolate."
The PM is also facing calls from senior members of his own backbenches, including former health secretary Jeremy Hunt, for a change to the system.
It comes as pub and restaurant bosses warned of a "summer of venue closures" unless hospitality workers are exempt from quarantine rules as cases continue to increase.
Iceland managing director Richard Walker said he was "deeply disappointed to see supermarket store workers omitted from the list".
Meanwhile, train timetables are being reduced across England to cope with last-minute cancellations due to staff isolating.
Transport for London warned of line closures and cancellations this weekend, with more than 300 members of staff isolating, while Thameslink, Southern and Avanti West Coast were among those slimming down services from Monday.
More than 600,000 people were alerted by the app in the week to 14 July.
And the latest information from the Office for National Statistics showed around one in 75 people in England currently have the virus.
On Thursday evening, the government published a list of 16 sectors where double-jabbed workers will be eligible to avoid isolation if they undergo daily lateral flow testing and their results are negative.
These included energy, civil nuclear, digital infrastructure, food production and supply, waste, water, veterinary medicines, essential chemicals, essential transport, medicines, medical devices, clinical consumable supplies, emergency services, border control, essential defence outputs, and local government.
And on Friday, the Department for Environment, Food and Rural Affairs expanded on this further, outlining the positions the exemptions would apply to "subject to all other mitigation options being exhausted".
The roles include manufacturing maintenance engineers, specialist reach truck drivers, official vets, environmental health officers, landfill operators, water engineers, laboratory staff essential to the batch release of medicines, and environment agency staff operating critical flood defence assets.
Those who work in the roles above will be able to leave their COVID-19 isolation to travel to work and do their jobs after a negative daily test but must remain at home otherwise and go straight into quarantine if they receive a positive result.
It will only apply to workers who are fully vaccinated - and 14 days after their second coronavirus jab.