Groups of up to six people will be allowed to meet outside provided they stay two metres apart as Boris Johnson announced a “cautious” easing of lockdown rules amid a continuing row over Dominic Cummings.

The Prime Minister confirmed that all five tests required for the next phase of restrictions to begin have been met, meaning more pupils can return to school and outdoor retail and car showrooms can open from Monday in England.

Mr Johnson outlined that people would be able to see “both parents at once, or both grandparents at once” in what he said would be a “long-awaited and joyful moment” for many.

The PM set out the details just hours after Durham Constabulary said they would have taken action if police officers had stopped Mr Cummings on his 50-mile round trip to Barnard Castle.

He said he regarded the issue as “closed” after the police said they did not intend to take “retrospective action”, though the force found that the aide may have committed “a minor breach” of lockdown rules in driving to the town.

Mr Johnson told the daily press conference that people should “try to avoid seeing too many households in quick succession so we can avoid the risk of quick transmission from lots of different families and continue to control the virus”.

“It remains the case that people should not be inside the homes of their friends and families, unless it is to access the garden.

“I should add that, at this stage, I am afraid that those who have been asked to shield themselves should continue to do so.”

Chief scientific adviser Sir Patrick Vallance stressed that the number of new infections is around one in a thousand per week – meaning that “54,000 new cases are occurring every week, so somewhere around eight or so thousand per day”.

He said: “That is not a low number, so it’s worth remembering that we still have a significant burden of infection, we are still seeing new infections every day at quite a significant rate and the R is close to one.

“That means there is not a lot of room to do things and things need to be done cautiously, step-by-step and monitored and the Test and Trace system needs to be effective in order to manage that.”

Chief medical officer Professor Chris Whitty said it was “really important” that people stayed two metres apart when meeting outside – saying that they would not be counted as a contact, and therefore would not need to self-isolate, if someone they met at a distance then developed coronavirus.

Mr Johnson blocked Sir Patrick and Prof Whitty from answering questions about the row over Mr Cummings to “protect them” from a “political argument”.

The PM said: “I’ve said quite a lot on this matter already and what I also note is that what Durham police said was that they were going to take no action and that the matter was closed.

“And I intend to draw a line under the matter, as I said yesterday to the Parliamentary Liaison Committee.”

He added: “I know that you’ve asked Chris and Patrick but I’m going to interpose myself if I may and protect them from what I think would be an unfair and unnecessary attempt to ask any political questions.”

Both advisers later said they did not wish to get involved in politics after being asked if they were comfortable with Mr Johnson telling them they could not answer questions about Mr Cummings.

Labour leader Sir Keir Starmer backed easing the restrictions, though he raised “serious concerns” about the level of statutory sick pay to support those asked to isolate.

And he accused the PM of having “totally misjudged” the nation’s mood over Mr Cummings, adding: “The weakness of the Prime Minister has meant a loss of a week when we should have been concentrating on what comes next.

“He should have acted, he was too weak to do so.”

In other developments:

– ONS figures suggest the average number of people with coronavirus in community settings in England remains “relatively stable”, though the infection rate among people working outside the home is around three times as high as for those working at home.

– Prof Whitty said it is hoped that “relatively soon” the number of infections will be low enough to start letting shielded people leave home.

– Mr Johnson said that from June 15 secondary schools will begin to provide “some face to face contact time” for years 10 and 12, while all shops will be able to open with social distancing measures in place.

– Contact tracers began tracking down people who have come into close contact with coronavirus sufferers, amid reports of major problems with the NHS Test and Trace system.

– Scottish First Minister Nicola Sturgeon announced that people in Scotland will be able to meet one other household at a time outdoors from Friday as lockdown measures ease.

– The toll of deaths linked to the virus rose to almost 48,000, while at least 189 frontline health and care workers have died after contracting Covid-19.

Durham Police said it did not consider Mr Cummings had committed an offence by locating himself at his father’s farm in the county.

But it noted that it was concerned with breaches of the regulations, not the general Government guidance to stay at home.

In its statement, the force said: “Durham Constabulary have examined the circumstances surrounding the journey to Barnard Castle – including ANPR (automatic number plate recognition), witness evidence and a review of Mr Cummings’ press conference on 25 May 2020 – and have concluded that there might have been a minor breach of the regulations that would have warranted police intervention.

“Durham Constabulary view this as minor because there was no apparent breach of social distancing.”

Durham’s former chief constable Mike Barton said he believed the force statement used the word “might” in relation to Mr Cummings breaking the regulations as they could not be seen to be acting as judge and jury.

Mr Johnson faced fresh cross-party calls for Mr Cummings to go in light of the police statement.