The Prime Minister and Chancellor Rishi Sunak – who also met Mr Javid on Friday – initially tried to get round the requirement to quarantine by saying they would join a workplace testing scheme.
But after a furious outcry with accusations of hypocrisy at a time when staff shortages due to people being forced to self-isolate were threatening supply chains, the two men hurriedly agreed to do so.
In a video statement posted on his Twitter feed, Mr Johnson said they had “briefly” looked at joining the daily contact testing scheme which is being trialled in the Cabinet Office and a number of other public and private sector organisations.
However, he added: “I think it is far more important that everybody sticks to the same rules and that’s why I’m going to be self-isolating until July 26.
“I know how frustrating it all is but I really do urge everybody to stick with the programme and take the appropriate course action when you are asked to do so by NHS Test and Trace.”
It means that Mr Johnson will be confined to his official country residence at Chequers when most lockdown measures in England are lifted on Monday.
Mr Sunak and Mr Javid will also be out of circulation, marking an inauspicious start to what ministers had hoped would be an “irreversible” end of statutory controls.
It came amid renewed warnings from scientists that case numbers – already running at more than 50,000-a-day – would continue to soar as mandatory social-distancing measures are lifted.
Professor Neil Ferguson – whose modelling led to the first lockdown in March 2020 – said they could reach 200,000 before the current wave of the pandemic finally peaked.
He said that could result in 2,000 hospital admissions a day leading to “major disruption” and further backlogs in NHS services.
Meanwhile businesses have warned of shortages on the shelves as the number of people off work after being pinged by the NHS Covid app continues to rise.
With growing reports of disruption to supply chains, public transport and the NHS, CBI president Lord Bilimora called for an immediate end to the requirement to self-isolate for people who have been fully vaccinated.
“Against the backdrop of crippling staff shortages, speed is of the essence,” he said.
Labour leader Sir Keir Starmer said the Government was in “chaos” at a time when it needed to maintain public confidence.
“Boris Johnson and Rishi Sunak have been busted yet again for thinking the rules that we are all following don’t apply to them,” he said.
“The way the Prime Minister conducts himself creates chaos, makes for bad government and has deadly consequences for the British public.
“They robbed the bank, got caught and have now offered to give the money back.”
Following confirmation late on Saturday that Mr Javid had tested positive, Downing Street announced early on Sunday morning that Mr Johnson and Mr Sunak would be joining the pilot testing scheme rather than isolating.
But within three hours they had dramatically changed tack and said the two ministers would be following normal rules on self-isolating.
Mr Sunak said that while the pilot was “fairly restrictive” allowing only essential government business, he recognised that “even the sense that the rules aren’t the same for everyone is wrong”.
To compound the embarrassment, Transport for London, one of the organisations which No 10 said was also taking part in the pilot, said that it had yet to receive formal notification that it was part of the trial.
A spokesman said: “The current Test and Trace rules on self-isolation have led to vital control room staff being unable to come to work, causing disruption on some Tube lines.”
Mr Johnson meanwhile defended the decision to go ahead with the unlocking as he appealed to people to be cautious when it came to exercising their new freedoms.
“We have got to remember that this virus is, sadly, still out there. We can see the stream of contagiousness of the Delta variant,” he said.
“But there is no doubt at all that the massive vaccination programme has very severely weakened the link between infection and hospitalisation, and between infection and serious illness and death.”