"With hindsight I should have sent everyone back inside. I should have found some other way to thank them," Boris Johnson said as he addressed MPs
Mr Johnson told MPs that he was only in the garden for 25 minutes to thank assembled staff before resuming work in his office.
But an email, leaked to ITV News - showed 100 staff were invited to attend "socially distanced drinks" in the Number 10 garden to "make the most of the lovely weather" - suggesting it was not intended to be a work meeting.
Here is his full apology delivered at the start of Prime Minister’s Questions:
Mr Johnson said: “I want to apologise. I know that millions of people across this country have made extraordinary sacrifices over the last 18 months.
“I know the anguish they have been through – unable to mourn their relatives, unable to live their lives as they want, or to do the things they love.
“I know the rage they feel with me and with the government I lead when they think in Downing Street itself the rules are not being properly followed by the people who make the rules.
“And though I cannot anticipate the conclusions of the current inquiry, I have learned enough to know there were things we simply did not get right and I must take responsibility.
“No 10 is a big department with a garden as an extension of the office which has been in constant use because of the role of fresh air in stopping the virus.
“When I went into that garden just after 6pm on May 20, 2020, to thank groups of staff before going back into my office 25 minutes later to continue working, I believed implicitly that this was a work event.
“With hindsight I should have sent everyone back inside. I should have found some other way to thank them.
“I should have recognised that even if it could be said technically to fall within the guidance, there are millions and millions of people who simply would not see it that way, people who have suffered terribly, people who were forbidden from meeting loved ones at all inside or outside, and to them and to this House I offer my heartfelt apologies.
“All I ask is that Sue Gray be allowed to complete her inquiry into that day and several others so that the full facts can be established.
“I will of course come back to this House and make a statement.”