Boris Johnson has defended his policy on coronavirus self-isolation in the face of a backlash from business and warnings it will lead to millions of people being forced to stay at home.

The Prime Minister has promised to tear up most of England’s coronavirus regulations at Step 4 of the road map, expected on July 19, but a major relaxation of self-isolation rules will not be brought in until August 16.

The expected surge in cases as a result of restrictions being lifted is predicted to lead an increase in contacts being “pinged” by the NHS Covid-19 app or being told by contact tracers to isolate.

Mr Johnson told MPs: “All these decisions are a balance of risk. This is a highly contagious disease. We have to do what we can to stop its spread.

“We have been looking at all the data and trying to strike the right balance. You could say we are going to dispense altogether with self-isolation and move straight to a testing regime.

“The difficulty with that is that you would effectively be allowing many more people to be vectors of disease than by continuing with our plan.”

From August 16, people in England who have received both doses of a vaccine – as well as the under-18s – will no longer have to self-isolate if they have been in contact with someone who tests positive for Covid-19.

Iceland supermarket boss Richard Walker said the difference between lockdown being lifted and self-isolation rules being eased would result in a “shit show for business”.

“Our Covid-related absences are growing exponentially,” he said.

“Within a week or two they’ll be the highest ever.”

Hospitality chiefs have warned that the delay between restrictions being lifted and the self-isolation rules being eased risks “the summer being cancelled and vast swathes of the population unnecessarily confined to their homes”.

Kate Nicholls, boss of trade body UKHospitality, said: “This is not just a hospitality issue – it is affecting the whole economy and we need an earlier test to release system in place.”

Helen Dickinson, chief executive of the British Retail Consortium, called for the August 16 date to be brought forward.

“We are already seeing a serious impact on retail operations as a result of staff having to self-isolate and this will only get worse right across the economy, as cases are already rising fast and the final restrictions are eased,” she said.

At Prime Minister’s Questions, Mr Johnson refused to say how many contacts he expected to be required to self-isolate before the changes are introduced.

“What we will be doing is moving away from self-isolation towards testing over the course of the next few weeks, and that is the prudent approach,” he told MPs.

Mr Johnson has acknowledged there could be 50,000 cases a day by July 19 and ministers have warned this could rise to 100,000 later in the summer.

Wednesday saw a further 32,548 lab-confirmed Covid-19 cases in the UK, the highest daily reported total since January 23, and a further 33 deaths.

The number of Covid-19 patients in hospital in England stood at 2,144 as of 8am on Wednesday, according to the latest figures from NHS England – up 43% from a week earlier and the highest number since April 10.

And a total of 416 hospital admissions of people with Covid-19 in England were reported for Monday, NHS England also said, up 70% from a week earlier and the highest number since March 15.

In response to questioning from Labour leader Sir Keir Starmer, Mr Johnson said scientists are “absolutely clear that we have severed the link between infection and serious disease and death” as a result of the vaccination programme.

But on Monday the Government’s chief scientific adviser Sir Patrick Vallance was more cautious, saying “vaccines have weakened the link between cases and hospitalisations, but it’s a weakened link, not a completely broken link”.

Despite the increased cases, Mr Johnson told the Liaison Committee of senior MPs that  “it looks as though” Step 4 of England’s road map out of lockdown will go ahead as planned on July 19.

Free market think tank the Adam Smith Institute predicted 100,000 daily cases would result in 3.5 million people a week being forced to self-isolate.

But the think tank’s projections were for an even higher level of daily infections, up to 133,000 by August 4, which would result in 4.6 million a week self-isolating.

Professor Christophe Fraser, from Oxford University’s Nuffield Department of Medicine -, who advises NHS Test and Trace, told Times Radio: “At the moment the epidemic is growing exponentially; we know that exponential (growth) very rapidly leads to big numbers – we’re two doublings away from 100,000 cases a day. And the doubling rate has been consistently between nine and 11 days so that’s not a lot of time ahead.

“And we don’t know when that’s going to peak – the different models have different projections, there’s considerable uncertainty at what stage the epidemic is going to peak.”

He added that 100,000 cases a day “would result in a large amount of people being traced”.

Meanwhile, Heathrow will provide fast-track lanes for some fully-vaccinated arrivals as the airline industry steps up pressure on ministers to open up quarantine-free travel to amber destinations.

The move comes ahead of an expected announcement on Thursday when Transport Secretary Grant Shapps will set out details of the Government’s plans to end the requirement for travellers from amber list countries to self-isolate on arrival.