This means they will be able to stay overnight with their partners for the first time since the lockdown began more than 11 weeks ago.
The new system of “support bubbles” will also allow single parents and isolated grandparents to go and stay with their children or have their grandchildren to stay at their own homes to help with childcare without any two-metre social distancing.
The prime minister also stated that if any members of a bubble come down with coronavirus symptoms, all members of it will have to self-isolate for 14 days as per current advice.
Speaking at Number 10’s daily press conference, Mr Johnson said: “I know how difficult the past months have been for people cut off from their friends and family.
“Last monday we relaxed the rules on meeting outdoors so that groups of six could gather provided they are socially distant.
“We did so in the knowledge that the transmission rate is much lower outdoors, so we could make this change in a safe way.
He added: “There are too many people, particularly those who live by themselves who are lonely and struggling with being unable to see friends and family
“So from this weekend we will allow single we will allow single adult households – adults living alone, or single parents with children under 18 – to form a support bubble with one other household.”
But, he warned: “We’re making this change to support those who are particularly lonely as a result of lockdown measures.
“It’s a targeted intervention to limit the most harmful effects of the current social restrictions.”
He warned it was “emphatically not” designed for people who don’t qualify “to start meeting in each other’s homes”, warning that remains against the law.
It comes as the UK’s coronavirus death toll increased by 245, bringing the total to 41,128.
The Department of Health and Social Care (DHSC) said 41,128 people had died in hospitals, care homes, and the wider community after testing positive for the deadly disease.
Out of the 6,042,622 tests that have been carried out in the UK, 290,143 cases have been confirmed positive.