Downing Street parties: Dominic Cummings will be interviewed as part of Cabinet Office investigation

Dominic Cummings will be interviewed as part of an investigation into parties and gatherings at Downing Street during coronavirus restrictions.

Boris Johnson's former chief adviser confirmed to Sky News that he will be involved in the probe, which is looking at events in Number 10 and other government departments.

Tory MP predicts PM will be gone in 'one week' - partygate latest

And a Cabinet Office source told Sky News: "If we reach the end of the investigation and the inquiry hasn't spoken to Dominic Cummings, eyebrows would be raised."

PM maintains he wasn't told about drinks event

The confirmation that Sue Gray will speak to Mr Cummings comes after he alleged that the prime minister knew in advance about a Downing Street drinks party in May 2020 and agreed that it could go ahead.

These claims have been confirmed to Sky News by a second source, but Number 10 continues to deny that Mr Johnson was told ahead of the event.

The PM maintained this stance on Tuesday, saying in an interview that "nobody told me" the garden party was "against the rules".

Mr Johnson's principal private secretary Martin Reynolds emailed officials with an invite to the event, suggesting attendees "bring your own booze!".

At the time, the public were only allowed to meet one other person not from their household in a public space outside, with indoor mixing still banned.

Cummings says PM 'lied to parliament'

In an updated post on his Substack page on Monday, Mr Cummings said he warned Mr Reynolds that his email "broke the rules" and also raised his concerns directly with the PM.

"I said to the PM something like: 'Martin's invited the building to a drinks party, this is what I'm talking about, you've got to grip this madhouse'," he wrote.

"The PM waved it aside."

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He added: "The events of 20 May alone, never mind the string of other events, mean the PM lied to parliament about parties.

"Not only me but other eyewitnesses who discussed this at the time would swear under oath this is what happened."

MP gives PM 'a week' before he's out

The 20 May event is the latest in a string of reported gatherings in Downing Street and other government departments during COVID restrictions in 2020 and 2021 that is being investigated.

Among the latest to make headlines were two parties held in Downing Street on the eve of Prince Phillip's funeral last year.

The disclosures have led to calls from opposition parties - and six Conservative MPs so far - for Mr Johnson to resign.

And the pressure on the PM shows no sign of abating, with one Tory telling Sky News that things are "nearly there" in terms of reaching the required 54 letters from MPs to trigger a leadership vote.

They described the past weekend as a "turning point" and said they give the PM "a week" before he is gone.

Another told political correspondent Joe Pike that the PM looked "absolutely beaten" in his latest interview, describing his performance as "awful" and like a "bad amateur dramatics performance".

Meanwhile, deputy political editor Sam Coates has been told that "lots of conversations" are happening between 2019 intake Tory MPs and there is a "resolve" among them that Mr Johnson should go.

"But there's a fear if the vote of no confidence comes before the Sue Gray report is out then Boris Johnson might win, and he could be safe for a year. They think things might not move before then," Coates added.

A government source hit out at these reported manoeuvres, telling Sky News: "Most of them [the 2019 intake] rode in on Boris Johnson's coattails and without him they'll be dumped pretty quickly.

"They don't know what they're doing, they don't realise how lucky they are. They're working against us, doing Labour's job for them".