John Swinney said the video footage, which shows No. 10 aides taking part in a mock press conference and joking about a “fictional” party in December 2020, is “one of the most appalling things” he had seen in his political career.
He also raised concerns that it could make people less likely to follow new Covid-19 restrictions, if these have to be imposed over the festive period to counter the spread of the new Omicron variant.
The UK Government has insisted there was no Christmas party and that coronavirus rules have been followed at all times.
But footage obtained by ITV shows the Prime Minister’s then-press secretary Allegra Stratton and adviser Ed Oldfield apparently taking part in a mock press conference in the media room at 9 Downing Street, in which Ms Stratton was questioned about the alleged event.
Asked if he is concerned that events in Downing Street could affect public compliance with any restrictions that may have to be imposed this Christmas, Mr Swinney told BBC Radio Scotland’s Good Morning Scotland programme: “You bet I am.”
The Deputy First Minister, who is also the Scottish Government’s Covid recovery secretary, added: “That video last night is just one of the most appalling things I have seen in my political life.
“I think it shows contempt at the heart of Downing Street for members of the public and that is exactly what you do not need at a time of national emergency and of the gravity that we face.
“So the experience that all of us are having to wrestle with in the handling of coronavirus, and particularly Omicron, are dealt a very serious blow by the appalling behaviour by Downing Street, by UK Government ministers who have quite clearly lied to the public about this party, and we need to recognise the seriousness of the threat that poses to our efforts on tackling coronavirus.”
His comments came as he warned “difficult decisions” might have to be taken in a bid to combat the spread of the new Omicron variant, which appears to spread more quickly than other forms of Covid-19.
The emergence of Omicron means “the virus is reinvigorated and reinvigorated at pace”, Mr Swinney said, adding this “poses a threat to us as a society”.
He added: “We’re trying to take all the steps we possibly can do without disrupting people’s expectations over the next few weeks, but I have to be candid with people that we face some difficult discussions in the weeks ahead.”
First Minister Nicola Sturgeon has already revealed the situation is now being reviewed on a daily basis, with Mr Swinney stating that restrictions may have to be reimposed as a result.
Ministers want to “avoid that if we possibly can”, the Deputy First Minister added, saying this is why the Scottish Government is urging people to act now, by working from home where possible and testing themselves for Covid using lateral flow devices before going out.