People living alone in England will be able to stay at one other household as part of a further easing of coronavirus restrictions.
Prime Minister Boris Johnson announced that, from Saturday, single adults can spend the night at another house in a "support bubble".
No 10 said the change aims to help combat loneliness and that people are being trusted to observe the rules.
The relaxation does not apply to those who are shielding, or other UK nations.
The PM also announced a new national "catch-up programme" for school pupils in England, after it was confirmed most children will not return to classrooms until September.
Mr Johnson told the daily Downing Street briefing the new "support bubbles" apply to single adult households or single parents with children under 18.
"All those in a support bubble will be able to act as if they live in the same household, meaning they can spend time together inside each others' homes and do not need to stay two metres apart," he said.
He added: "I want to stress that support bubbles must be exclusive, meaning you can't switch the household you are in a bubble with or connect with multiple households.
"And if any member of the support bubble develops symptoms, all members of the bubble will need to follow the normal advice on household isolation."
How might "support bubbles" work?
The government gave examples for how the new "support bubbles" might work for single adults in England:
- A grandparent who lives alone would be able to form a bubble with one of their children, which means they could go to see them and interact with their grandchildren as normal
- A single parent could form a bubble with a parent or friend so they can interact as normal
- Two single people who both live on their own could form a bubble
- And a couple who do not live together could form a bubble, but only if they both live alone
No 10 also said that if a person lives alone but their partner has a flatmate, for example, then they can form a bubble but the flatmate cannot then form their own with another household.
If anyone within a bubble develops coronavirus symptoms, everyone within the bubble must self-isolate for 14 days.
There were 8.2 million people living alone in the UK last year, according to the Office for National Statistics, with just under half aged 65-and-over. There were also 2.9 million single-parent households.
Who can't create a "support bubble"?
Mr Johnson said the new rule is "not designed for people who don't qualify to start meeting inside because that remains against the law".
One part of the bubble has to be a single household, or be a single parent to children aged under 18.
It does not apply to grandparents who live together, people living in houses of multiple occupancy, such as flat shares, or to couples who already live together.
Those who are shielding cannot be advised to form a bubble, the PM said.
He added: "However, I want to say I know how hard it is for those of you who are shielding and we will say more next week about the arrangements that will be in place for you beyond the end of June."
Boris Johnson is keen to emphasise the government is moving slowly in easing the lockdown.
The "support bubble" plan is very limited - designed to help the loneliest in England.
It's the government dipping another very tentative toe into the water when it comes to easing distancing restrictions.
But just as lockdown is eased further, questions are increasing about the decisions we've seen so far.
Comments from Prof Neil Ferguson on lockdown coming too late will be very uncomfortable reading for those in power, even if they can say they were acting on the advice they were getting.
Likewise, England's chief medical officer saying testing could have been ramped up earlier will be seized upon by the government's critics.
The government doesn't want to talk about its early decisions yet - but many others already are.
The BBC's Laura Kuenssberg asked why children will soon be able to go and look at lions in a zoo but may not be able to return to the classroom until September.
Mr Johnson said the government had wanted to get the remainder of primary pupils back before the summer holidays.
But the circulation of coronavirus was "not quite down far enough to change the social distancing measures that we have in our schools".
"What we'll be doing is a huge amount of catch-up for pupils over the summer months," he pledged, adding that Education Secretary Gavin Williamson "will be setting out a lot more next week about the catch-up programme".
He defended the approach on schooling by comparing England's policy to other European countries.
And he said a return for all pupils in September depended on progress continuing in controlling the virus.
Earlier, Prof Neil Ferguson, a former government science adviser, told MPs deaths in the UK would have halved had the country entered lockdown a week earlier.
Asked about the comments at the government briefing alongside the PM, the UK's chief medical adviser Prof Chris Whitty said people would have different views on when the lockdown should have been introduced.
He said there was "very limited" information about the virus at that stage and we now know more.
The PM said: "It's too early to judge ourselves. We know a lot more about the virus than we did in January, February or even March.
"You have to proceed with caution, that is what we are doing."
The UK government's chief scientific adviser Sir Patrick Vallance said the R number - the number of people an infected person passes the virus on to - remains "just below one".
"The epidemic is shrinking, but not fast," he said. "Numbers are coming down but are not yet very low."
Mr Johnson also confirmed there have been a further 245 coronavirus deaths across all settings in the UK, taking the UK death toll to 41,128.
The pandemic has, effectively, become a game of risk management - that's because, as Prof Witty says, nothing is "risk free".
We could continue to suppress the virus by not easing lockdown any further.
That would further reduce the spread of coronavirus - and no doubt save lives.
But it would come at a huge cost economically, socially, to children's education and also to people's health, whether it is from mental or physical illness linked to continued strict curbs.
Instead, the fine line being trod by the government and its advisers is to navigate a way through this (whether they are doing a good job or not is a whole other question).
The aim is to keep the spread of the virus low, while reopening society.
Whatever is done, there will be victims.
In the end it will come down to both political judgements, in terms of how quickly restrictions continue to be lifted, and also individual judgements, in terms of how quickly we each embrace the new freedoms.
That, unfortunately, is the way life is in this pandemic.