ITV News UK Editor Paul Brand broke the story on Monday about an email providing the first evidence of a party on May 20, 2020 in the Number 10 garden
Boris Johnson has been accused of "lying to the British public" by Labour Leader Sir Keir Starmer after ITV News revealed a leaked email proving a party was held in Downing Street at the height of the UK's first coronavirus lockdown.
The prime minister has so far refused to comment on allegations that he and wife Carrie attended the party on May 20, 2020, claiming an investigation into Downing Street lockdown breaches prevents him from doing so.
But he's previously insisted that rules were always followed in Downing Street throughout the pandemic and responding to the latest allegation, he said: "All that, as you know, is the subject of a proper investigation by Sue Gray."
Labour Leader Sir Keir said in a tweet that the PM's "deflections and distractions are absurd".
"Not only did you know about the parties in Downing Street, you attended them. Stop lying to the British public. It's time to finally come clean."
Labour has been granted an Urgent Question in the House of Commons on Tuesday, requesting the PM to make a statement to MPs about the party.
The rules of Parliament mean a member of the government must respond to the question, and despite Labour hoping the prime minister will answer, paymaster general Michael Ellis will instead.
Downing Street has given its backing to the man who sent the email invite, Mr Johnson's Principal Private Secretary Martin Reynolds, saying he "continues in his role" and has the full confidence of the PM.
The prime minister's decision to not comment was backed by Health Minister Ed Argar, sent out to defend the government in a round of broadcast interviews, who said it is "right" top civil servant Ms Gray is given space to investigate.
"The prime minister is respecting the integrity of this investigatory process. He is not going to comment while this investigation is underway."
The latest allegations against Number 10 come after the PM's former top adviser wrote a blog post in which he said a party was held in May 2020 and there was an email chain to prove it.
'Bring your own booze': The email inviting No10 staff to a lockdown party
The email invite, which was exclusively shared with ITV News, told over 100 people they could attend a garden party in Downing Street but they had to bring their own alcohol.
The email was sent by Mr Reynolds to Number 10 employees including the prime minister's advisers, speechwriters and door staff all invited.
ITV News understands around 40 staff gathered in the garden that evening, eating picnic food and drinking. Crucially, they included the PM and his wife Carrie Johnson.
In the letter sent to staff, Mr Reynolds - a senior No 10 civil servant who has run Boris Johnson's private office since October 2019 - says:
"After what has been an incredibly busy period we thought it would be nice to make the most of the lovely weather and have some socially distanced drinks in the No10 garden this evening.
"Please join us from 6pm and bring your own booze!"
Will police investigate?
The Cabinet Office inquiry into allegations of various parties and events is currently being carried out by senior civil servant Sue Gray, who took over from the Cabinet Secretary Simon Case due to allegations that he knew of at least one party himself.
'He's lied to you': What angry MPs are saying:
Lib Dem leader Sir Ed Davey also blasted the prime minister on LBC on Tuesday morning, branding the latest scandal "the worst".
"I'm concerned about the lies that Boris Johnson has told Parliament," Sir Ed said and added Mr Johnson has "lied to the public, he's lied to you, he's lied to Parliament it appears."
He also said: "We kept to the rules that Boris Johnson's said we should keep to, and now we hear he was partying!"
Ruth Davidson, former leader of the Scottish Conservative Party, also tweeted: "Nobody needs an official to tell them if they were at a boozy shindig in their own garden.
"People are (rightly) furious. They sacrificed so much - visiting sick or grieving relatives, funerals. What tf were any of these people thinking?"
Labour also pointed to a number of times the prime minister denied breaking lockdown rules.
When asked about Downing Street Parties in the Commons in December the prime minister said: "All the guidelines were observed...
"I apologise for the impression that has been given that staff in Downing Street take this less than seriously.
"I am sickened myself and furious about that, but I repeat what I have said to him: I have been repeatedly assured that the rules were not broken."
Who is the 'we' in the invite and what next for the prime minister? UK Editor Paul Brand and Political Editor Robert Peston explain
The latest revelations have led to fresh calls for the prime minister to be questioned as part of the internal inquiry into a series of parties in Downing Street, launched after ITV News aired footage of Number 10 staff laughing and joking about an event on December 19 2020.
In that video, the prime minister's then spokesperson Allegra Stratton suggested that there had been "no social distancing" at the event, which staff jokingly referred to as a "business meeting" with "cheese and wine".
ITV News obtained exclusive footage of senior Downing Street staff joking about holding a Christmas party in a mock televised press briefing