Isolation rules will be relaxed for a “small number” of fully-vaccinated critical workers who are identified as close contacts of coronavirus cases, Boris Johnson has said after coming under sustained pressure over the “pingdemic”.

The Prime Minister on Monday resisted widespread calls to announce a more wide-reaching change to the rules to reduce the number of people in isolation, as he addressed the public from his own quarantine on so-called “freedom day”.

He described self-isolation as “one of the few shots we have got left in our locker”, on the day he scrapped most remaining legal restrictions and defended the timing, despite cases soaring.

But he warned nightclubs and other venues with large crowds must make full vaccination a requirement of entry from the end of September.

Speaking virtually from his Chequers retreat, Mr Johnson said it was necessary to keep the isolation rules largely unchanged until August 16, when a testing regime will replace the requirement for fully-vaccinated contacts to isolate.

But he added: “In the meantime I want to assure you that we will protect crucial services, including the staffing of our hospitals and our care homes, the supplies of food, water electricity and medicines, the running of our trains, the protection of our borders, the defence of our realm, by making sure that a small number – a very small number – of named fully-vaccinated critical workers are able to leave their isolation solely for the the work that I have described.

“But for the vast majority of us, myself included, I’m afraid we do need to stick with this system for now.”

Some 17 hours after nightclubs reopened for the first time since March last year, chief scientific adviser Sir Patrick Vallance warned they had the potential to cause “super spreading events”.

Mr Johnson, despite having previously billed his lockdown-easing plan as “irreversible”, now said that “I don’t want to have to close nightclubs again as they have elsewhere” as he urged them to use the NHS Covid Pass for entry, despite it not currently being a legal requirement.

“I should serve notice now that by the end of September, when all over 18s will have had the chance to be double jabbed, we are planning to make full vaccination the condition of entry to nightclubs and other venues where large crowds gather,” he said.

“Proof of a negative test will no longer be sufficient.”

Mr Johnson said that “I certainly don’t want to see passports for pubs” but declined to rule out the possibility of introducing them.

Speaking in the Commons, vaccines minister Nadhim Zahawi gave more details on the incoming exemption for self-isolation, which already covers frontline NHS staff and social care workers.

Mr Zahawi said the change would cover the police, air traffic controllers and train signallers, and others in “circumstances where there would be a serious risk of harm to public welfare if people in critical roles are unable to go to their workplace”.

“So people in those kinds of roles, who have received two vaccinations plus two weeks beyond the second vaccine, will not need to self-isolate for those critical tasks,” he added.

The Government said it is “not a blanket exemption for any sector or role”, only applying to named individuals, and said departments will be writing to employers to explain their next steps.

The British Retail Consortium called for clarity on who would be exempt, and said retail workers and suppliers should be included for the “vital role” they have played in the pandemic.

Chief executive Helen Dickinson said: “While it is good that Government recognises the problems that are being created by an overzealous track and trace system, it remains unclear who will be covered under the new list of critical workers.

“With community cases soaring, the number of healthy retail staff having to self-isolate is rising fast, threatening to disrupt retail operations, and potentially close shops or distribution centres.”

A Government spokesman said: “This is not a blanket exemption for any sector or role. Decisions to inform an employer that designated critical workers are considered to have a reasonable excuse to attend work will be made by the relevant department with responsibility for the critical service.

“The employer will receive a letter from that Government department informing them and telling them what steps they must follow.”

The Prime Minister was self-isolating in his official country residence after Health Secretary Sajid Javid tested positive for Covid-19.

Mr Johnson and Chancellor Rishi Sunak initially tried to avoid quarantining after being contacted by NHS Test and Trace, by saying they were taking part in a testing pilot.

But in the face of mounting public fury they made a swift U-turn, which meant three of the most senior ministers were among those in quarantine on “freedom day”.

Mr Johnson insisted he did not think he was above the rules, following the aborted plan that would have allowed him to continue working from Downing Street instead of self-isolating.

“I absolutely didn’t think that,” he told the press conference. “I am today on Zoom or Teams or whatever brilliant system it is that we are using.”

Hospitality, leisure, food production and retail sectors have complained of having to close premises or slash opening hours because of the number of people being told to stay at home for 10 days after being in contact with a person who has tested positive.

Andrew Lloyd Webber was among those to warn that “freedom day has turned into closure day” after the cancellation of performances of his West End show Cinderella.

But Downing Street said there are no plans to reduce the sensitivity of the NHS Covid-19 app responsible for some of the isolation requests by issuing “pings” over close contacts.

Mr Johnson acknowledged it is “frustrating” but said the public had to accept increasing numbers would be told to isolate “as a consequence of living with Covid”, saying those identified as contacts are at least five times more likely to be infected than others.

Clubs were quick to condemn his proposal to introduce vaccine passports in the autumn, arguing they are difficult to enforce and will reduce the amount of passing trade.

Michael Kill, chief executive of the Night Time Industries Association, said: “So, ‘freedom day’ for nightclubs lasted around 17 hours then.

“What an absolute shambles.”

Labour leader Sir Keir Starmer has called the wholesale easing of most restrictions “reckless”, while Scotland’s First Minister Nicola Sturgeon said talk of “freedom day” is “not sensible” given the UK is recording around 50,000 new Covid cases per day.

A further 39,950 lab-confirmed cases were announced in the UK on Monday, along with an additional 19 deaths within 28 days of a positive Covid test.

Meanwhile, the Health Secretary announced that children who are at increased risk of Covid-19 are to be offered the Pfizer vaccine “as soon as possible”, as are those living with people with weakened immune systems.

Those aged 12 to 15 with conditions including Down’s syndrome, immunosuppression, multiple or severe learning disabilities will get access to vaccines.

So too will people aged 12 to 17 who live with someone who is immunosuppressed, such as a parent or grandparent.