Boris Johnson is facing growing pressure to allow fully vaccinated people who have been identified as close contacts of coronavirus cases to be exempt from isolation.

London Mayor Sadiq Khan has joined business leaders in calling for more 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 for a change to the system.

Conservative MP and chairman of the health and social care select committee Jeremy Hunt warned the government that it faces “losing social consent” for the self-isolation scheme if nothing is done.

And fellow Conservative Greg Clark, a former business secretary who now chairs the Commons science and technology committee, suggested that an exemption from self-isolation for all those fully-vaccinated should be brought in immediately.

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.

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.

Business Secretary Kwasi Kwarteng admitted the government is “very concerned” about the numbers of people being pinged by the NHS app.

From 16 August, all of those double vaccinated will be exempt from self-isolation if identified as a close contact, the government has said.

Environment Secretary George Eustice told Sky News this date “at the moment is not coming forward”.

The PM himself is currently isolating at Chequers, having been identified as a close contact of newly-appointed Health Secretary Sajid Javid who tested positive for coronavirus.

Chancellor Rishi Sunak was identified as another of Mr Javid’s contacts – and Labour leader Sir Keir Starmer was also forced into isolation on Wednesday after one of his children tested positive for 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.

Around 10,000 workers in the food sector are also expected to be included in the scheme.

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.