Couples kept apart by lockdown restrictions could be reunited and some grandparents will be able to hug their grandchildren from Saturday under plans set out by Boris Johnson.

The Prime Minister’s plan for “support bubbles” will allow adults living alone or single parents to mix with one other household.

They would then be allowed to interact as though they were one household, spending time together indoors, not having to follow the two-metre rule and would be allowed to stay overnight.

As the latest move to ease England’s coronavirus restrictions was announced, an expert who had advised the Government suggested that imposing the lockdown a week earlier in March could have halved the death toll.

Professor Neil Ferguson’s comments came as the number of deaths involving Covid-19 in the UK passed 52,000, according to analysis of the latest available data.

Officials admitted the support bubble measure announced by the Prime Minister was not going to benefit everyone but was targeted at those who had been left isolated by the lockdown restrictions.

It could allow children in single-parent households to see one set of grandparents.

A grandparent living alone would be allowed to visit the house of their child and grandchildren.

But the move would not allow a couple to visit both parents as neither household would comprise a single adult.

At the Downing Street briefing, the Prime Minister said: “We are making this change to support those who are particularly lonely as a result of lockdown measures.”

Prof Ferguson, from Imperial College London, told the Commons Science and Technology Committee the actions which saw a lockdown finally imposed on March 23 were based on what was known about the virus at the time.

He said: “The epidemic was doubling every three to four days before lockdown interventions were introduced.

“So, had we introduced lockdown measures a week earlier, we would have reduced the final death toll by at least a half.

“So whilst I think the measures, given what we knew about this virus then in terms of its transmission and fatality, were warranted, certainly had we introduced them earlier we would have seen many fewer deaths.”

Prof Ferguson’s modelling of the infection was instrumental in the lockdown being introduced but he later quit the Scientific Advisory Group for Emergencies (Sage) panel advising ministers after flouting the restrictions.

Asked about Prof Ferguson’s claim, Mr Johnson said “all such judgments will need to be examined in the fullness of time”.

The need to continue on the path out of lockdown was underlined by warnings the UK is on course to suffer the biggest economic hit of any developed country from the coronavirus.

The Organisation for Economic Co-operation and Development (OECD) said Britain’s economy was likely to slump by 11.5% in 2020 – but could contract by 14% if there is a second wave of Covid-19 later this year.

One barrier faced by firms wanting to reopen is the rule requiring people to stay two metres apart and Mr Johnson said it was being kept under review as the number of coronavirus cases comes down.

Professor Robert Dingwall, a sociologist on one of the scientific groups advising the Government, said studies into the two-metre rule’s impact did not take account of the “economic devastation” it caused.

The British Beer and Pub Association said it meant only a third of England’s pubs will be able to reopen when given permission to do so – currently July 4 at the earliest – with up to 25,000 left wondering when, if ever, they will be able to serve drinkers.

Mr Johnson said: “As we drive this disease down, as we get the incidence down, working together, I want to make sure that we keep that two-metre rule under constant review.”

In other developments:

– England’s chief medical officer Chris Whitty said he would have liked more testing in the early stages of the pandemic as “many of the problems that we have had came because we were unable to actually work out exactly where we were”.

– Private hospitals requisitioned by the state will carry out cardiac operations and perform chemotherapy to help reduce pressure on the health service after the NHS Confederation suggested around 10 million people will be on waiting lists by the end of the year.

– Mr Johnson announced a £63 million local welfare assistance fund to help “the most vulnerable families” but Labour said it only amounted to just over half the £115 million it would have cost to extend the school meal voucher scheme over the summer.

– There will be expanded and targeted coronavirus testing for frontline workers in “high-contact professions”, Mr Johnson said.

The Prime Minister continued to face pressure over the decision to abandon plans to get primary school children back in class before England’s summer break.

Mr Johnson acknowledged he was “moving slower than we would have liked in some areas”.

He added: “The rate of infection is not yet quite low enough and because we are not able to change our social distancing advice, including smaller class sizes in schools, we are not proceeding with our ambition to bring back all primary pupils.”

Mr Johnson’s appearance at the press briefing came on the eve of the 12-week deadline he set for the country to “turn the tide” in the battle with the virus.