In England, up to six people will be able to meet outside and schools will gradually reopen from Monday, Johnson said at a news conference where he was again challenged over his aide Dominic Cummings' decision to drive 400km during lockdown.

"These changes mean that friends and family can start to meet their loved ones, perhaps seeing both parents at once or grandparents at once," he said, adding that outdoor retailers and car showrooms would also be able to open from Monday.

"You could have meetings of families in a garden, you could even have a barbecue provided you did it in a socially distanced way, provided everybody washes their hands, provided everybody exercises common sense."

Johnson stressed that the changes were "small tentative steps forward", and health experts warned the situation remained finely balanced with new cases declining, but not very quickly.

The devolved governments in Scotland, Wales and Northern Ireland are responsible for their own public health policy.

Johnson's announcement came hours after more MPs from his Conservative Party called for Cummings to quit.

Cummings travelled from London to the northern English city of Durham in March with his four-year-old son and his wife, who was sick at the time, to be close to relatives.

A YouGov opinion poll showed a majority of Britons think Cummings should resign for - in their view - breaking the lockdown rules, but Johnson has said he acted with integrity.

Australian Associated Press