We're trying to strike the right balance, says Boris Johnson as he defends waiting until August 16 to end self-isolation rules

The Government has said people who are fully vaccinated will not have to self-isolate if they come into contact with someone who has tested positive for Covid-19 from August 16.

Giving evidence to the Commons Liaison Committee, the Prime Minister was pressed on suggestions that it could lead to an additional five million being forced to quarantine at home as a result.

Mr Johnson said: "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."

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 changes to 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 to millions of contacts being "pinged" by the NHS Covid-19 app or being told by by contact tracers to isolate.

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.

In a sign of business concerns, Iceland supermarket boss Richard Walker said the different timings would result in a "shit show" for firms.

"Our Covid-related absences are growing exponentially," he said. "Within a week or two they'll be the highest ever. Covid rules end 19 July. Self-isolation rules not eased until 16 August.

"This will be a shit show for business."

At Prime Minister's Questions, Mr Johnson refused to say how many contacts would 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 warned 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.

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".

As Sir Keir and Mr Johnson clashed in the Commons, the Prime Minister challenged the Labour leader to say whether he supported the planned lifting of restrictions on July 19.

Sir Keir said: "We should open up in a controlled way, keeping baseline protections such as masks on public transport, improving ventilation, making sure the Track and Trace system remains effective, and ensuring proper payments for self-isolation."

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: "With cases predicted to continue to rise, this means that hospitality's recovery after 16 months of lockdown and severely disrupted trading will be harmed."

Former Tory leader Sir Iain Duncan Smith said: "Why would you even go to a pub (after July 19)? This makes it worse."

He told the Daily Telegraph: "I wouldn't go to a pub that wasn't still having six around a table and social distancing, otherwise you run the risk of everyone in the pub being pinged and locked down."

Business Secretary Kwasi Kwarteng acknowledged "it's a balance, it's not a perfect solution" but told Sky News: "On the one hand we're saying that we can reopen and on the other we're saying that we want to give a little bit more protection in terms of the self-isolation rules."

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.

Mr Kwarteng played down that prospect, saying: "I don't think you can necessarily conclude there will be millions."

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".