Unlike outdoors, where restrictions were lifted last month, the chances of transmission through the air would still be “quite high”, he argued.
“You are at much greater risk because you are sitting in proximity to other people, you are not wearing masks if you are in pubs and restaurants,” Sir David warned.
“It only takes one or two individuals who are shedding the virus sitting near you – not even close to you – and you are at risk of getting the disease.”
The former scientific adviser, between 2000 and 2008, also insisted the official Scientific Advisory Group for Emergencies (Sage) opposed the changes, alongside his rival Independent Sage organisation.
“The government’s own science advisers are saying exactly the same thing.” Sir David said.
Mr Johnson is expected to reveal that cultural life in England will restart with museums, art galleries and cinemas – as well as pubs and restaurants – able to reopen from 4 July.
Visitors are expected to have to pre-book tickets for venues that will also have to introduce one-way systems, spaced queuing and improved ventilation.
Domestic holidays will return, with hotels, holiday homes and bed-and-breakfasts able to reopen as the two-metre social distancing rule is halved.
And the ban on people from different homes meeting together indoors is set to be eased, with two households likely to be allowed to mix.
Asked about the biggest lifting of restrictions since lockdown in March, Sir David said: “No, we don’t think it’s safe – this is far too premature.
Pointing to 1,000 new infections per day, he argued: “We would say ‘let’s go into lockdown now’ if we were at the beginning of the pandemic. To come out of it too early is extremely risky.”
And he added: “The second issue, and this is really just as important, is that we don’t yet have a functional test-and-trace system operating.”
‘If we are impatient, we are going to go back into lockdown and all the hard work will be undone.”
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