BORIS Johnson joined in a party at No10 during the first coronavirus lockdown, according to reports.

The Prime Minister told one at an event in May 2020 that they “deserved a drink for beating back the virus”, according to an investigation by The Independent and The Guardian.

The party allegedly saw food served and drinks including wine, beer, and spirits consumed both inside and outside the Prime Minister's official residence.

The reports have sparked fresh calls from the SNP for Johnson to step down, saying it is "beyond any doubt" that Downing Street repeatedly ignored rules it had laid down for others.

READ MORE: Nicola Sturgeon writes urgent plea to Boris Johnson over Covid support

The event was allegedly held on May 15, while the UK was in lockdown. At the time, Scotland was considering how to gradually lift the severe restrictions which had been in place since late March.

However, while the rest of the country reduced social contacts as much as possible in order to slow the spread of the coronavirus, Downing Street held an event for around 20 civil servants.

At the time, coronavirus rules in place forbade meetings indoors and only allowed for a maximum of two people from different households to meet outdoors - and they had to maintain social distancing.

The National: Health Secretary Matt Hancock during a media briefing in Downing Street

Matt Hancock - the disgraced health secretary who was in office at the time - also reportedly attended the party. However, a spokesperson for the Tory MP denied this was the case.

The party was allegedly held after Hancock gave a press conference urging people to "stay at home as much as is possible". Although there is no suggestion that he or the Prime Minister drank or stayed late, others in attendance reportedly kept drinking into the evening.

One source told the papers that the event had a "celebratory" air given the news that the UK would begin to look at lifting the strict lockdown rules in place.

On the day of the alleged party, the UK recorded 384 deaths linked to Covid-19, and had more than 10,000 people suffering with the disease in hospital.

READ MORE: BBC cuts off key Omicron update for news on Queen's Christmas lunch plans

The new allegations are the latest in a long line of reports which raise questions about a "one rule for them" culture at the top of Government.

Allegra Stratton, once Boris Johnson's press secretary, was forced to quit after a video emerged of her laughing and joking about a party held in the run up to Christmas 2020.

Johnson did not deny that an event took place on December 18, 2020 - but insisted no rules were broken despite the rules in place at the time having prohibited parties.

The row that has dominated the news agenda over lockdown-busting parties at No10 has also seen the Metropolitan Police threatened with legal action over their refusal to investigate the Tory government's breaches of its own legislation.

A Downing Street spokesperson told the Independent: "In the summer months Downing Street staff regularly use the garden for some meetings. On May 15, 2020 the Prime Minister held a series of meetings throughout the afternoon, including briefly with the then-health and care secretary and his team in the garden following a press conference.

“The prime minister went to his residence shortly after 7pm. A small number of staff required to be in work remained in the Downing Street garden for part of the afternoon and evening.”

Hancock's spokesperson said he had "left Downing Street at 6:32pm" that evening after having debriefed the Prime Minister on his work that day.

Responding to the reports, the SNP's newly re-elected Westminster leader, Ian Blackford, reiterated calls for Boris Johnson to resign.

The National: Ian Blackford

He said: "We are facing another challenging moment in this pandemic, but once again it is the Prime Minister's conduct in office that risks undermining our efforts in tackling the crisis.

"When people across the UK followed the rules in place in order to protect people's lives and protect our NHS, the Tories were allegedly flouting the rules and holding parties.

"When we clapped for carers and our NHS staff, the Tories clinked their champagne glasses.

"It's beyond any doubt that the reported Downing Street parties were not out of the ordinary or spontaneous, but that there were repeated offences. A culture of rule-breaking dominates this corrupt Tory government.

"The SNP has been clear that this Prime Minister has lost all authority and he has a duty to at long last do the right thing and resign."