* Johnson admits attending lockdown gathering
* Apologies, says understands the fury
* Opposition calls on Johnson to quit
* 'The Party's over prime minister,' Labour says (Adds more quotes)
By William James and Kylie MacLellan
LONDON, Jan 12 (Reuters) - British Prime Minister Boris Johnson offered his "heartfelt apologies" on Wednesday for attending a "bring your own booze" gathering at his official residence during the country's first coronavirus lockdown as opponents said he must resign.
Johnson admitted for the first time that he had attended the party at 10 Downing Street on May 20, 2020, when COVID-19 rules limited social gatherings to a bare minimum, and said he understood the anger the revelations had caused.
"I know the rage they feel with me over the government I lead when they think that in Downing Street itself the rules are not being properly followed by the people who make the rules," an ashen-faced Johnson told parliament.
Johnson, who won a landslide 2019 election victory on a promise to secure Britain's exit from the European Union, said he regretted his action and had thought the gathering was a work event - drawing jeers from opposition lawmakers.
"I went into that garden just after six on the 20th of May 2020 to thank groups of staff before going back into my office 25 minutes later to continue working," he said. "With hindsight, I should have sent everyone back inside."
Opposition Labour Party leader Keir Starmer said Johnson must now resign and that the public thought him a liar.
"The party's over, prime minister," Starmer told him.
"After months of deceit and deception, the pathetic spectacle of a man who has run out of road. His defence that he didn't realise he was at a party is so ridiculous that is actually offensive to the British public."
'PARTY IS OVER'
Anger has grown since ITV News reported Johnson and partner Carrie mingled with about 40 staff in the Downing Street garden after his Principal Private Secretary Martin Reynolds sent an email invitation asking attendees to "bring your own booze".
Numerous people, including some lawmakers, have described how the rules kept them from the bedsides of dying loved ones last May in contrast to the events in Downing Street.
Some of Johnson's own Conservative members of parliament (MPs) have said how he responded on Wednesday to the growing furore would determine his future.
"His survival is in the balance at the moment," said one senior Conservative MP, speaking on condition of anonymity due to the sensitivity of the situation.
Two snap opinion polls on Tuesday showed well over half of respondents thought Johnson should resign.
But while parliament resounded with demands for his head, Johnson's biographer Andrew Gimson said he was unlikely to quit unless forced out by his parliamentary colleagues.
"He will be looking for a way through this. He is not the resigning type," Gimson said.
When details of the gathering first emerged, Johnson said he could not comment until a senior government official, Sue Gray, concludes an internal investigation into other allegations that he and his officials held rule-breaking parties.
In response to the calls for his resignation, he again deferred to Gray's investigation.
"I cannot anticipate the conclusions of the current inquiry, I have learned enough to know that there were things we simply did not get right. And I must take responsibility," he said.
Just two years after Johnson's election triumph, and less than six after he led the Brexit campaign to victory in 2016's EU referendum, speculation about his leadership is now rife.
There are mutterings that Conservative MPs, who can trigger a leadership challenge if 54 of the 360 in parliament write letters of no confidence, are sharpening their knives.
Last month, the Conservatives lost a parliamentary seat they had held for almost 200 years while the party's comfortable lead over Labour in opinion polls has also evaporated.
A series of mis-steps and scandals https://www.reuters.com/world/uk/sleaze-scandal-lockdown-parties-trying-times-uk-pm-johnson-2022-01-11 and public anger over the government's handling of the COVID-19 pandemic, rising energy bills and concerns about surging inflation have fuelled Conservative unease.
(Additional reporting by Elizabeth Piper and Kate Holton; Writing by Michael Holden; Editing by Guy Faulconbridge and Catherine Evans)
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