- The paper says the video sheds new light on a gathering that police had previously looked into.
- The Conservative Party said four people seconded to Mr Bailey's campaign were disciplined.
A video has emerged showing some Conservative Party workers drinking and dancing at a Christmas party during the Covid pandemic.
In the video, published by the Mirror, one person is heard saying it is OK to film "as long as we don't stream that we're, like, bending the rules".
The paper says the video sheds new light on a gathering that police had previously looked into.
The Conservatives said disciplinary action had already been taken.
The video, taken at the Conservative party's headquarters in Westminster, dates from December 2020 when London was in Tier 2 restrictions.
This meant people were banned from socialising indoors, except with members of their household or a support bubble.
People in London who did want to socialise at that stage of the pandemic had to do so in a garden or at a pub with outdoor seating - but such gatherings were limited to groups of six people.
Police investigated the event last year and no fines were issued.
Shaun Bailey, who was given a peerage in Boris Johnson's resignation honours list this week, was running for London mayor in December 2020, and members of his campaign team attended this gathering inside the Tory party's HQ.
The event has been reported before, but only still photographs were published by the Daily Mirror. Although Mr Bailey was photographed surrounded by party workers in those images, he is not seen in this newly-obtained video.
In November 2022, Scotland Yard said it was taking no action against Mr Bailey nor other people who attended the gathering.
The Conservative Party said four people seconded to Mr Bailey's campaign were disciplined.
In the 45-second video on the Mirror website, people can be seen drinking and standing in groups, while a man and a woman can be seen holding hands and dancing.
Cabinet minister Michael Gove said he would like to "apologise to everyone" over the video, adding it was "terrible" and "completely out of order".
"The fact this party went ahead is indefensible," he told Sky News.
Labour's Angela Rayner said the attendees had "openly mocked" the rules of Covid pandemic.
"The Tories think it's one rule for them and one rule for everyone else," added the deputy leader.
Liberal Democrat deputy leader Daisy Cooper Tory MPs and ministers should be "sick to their stomachs" seeing this new footage.
"While families grieved and NHS staff worked on the front line, Conservative Campaign Headquarters partied."
The Metropolitan Police have not yet responded to the new video footage.