British Prime Minister Boris Johnson has announced a coronavirus ‘Plan B’ as the UK faces a surge in cases and the spread of Omicron.

But all eyes are on his team’s own approach to COVID-19 rules.

Early on Thursday morning, one of the PM’s staffers burst into tears as she promised to resign after video emerged of her joking about a Christmas party held during lockdown – on a day over 400 people in the UK died of the coronavirus.

Mr Johnson had been insisting his staff had not broken rules and that a party never happened at Downing Street before Christmas last year. But he has now apologised, saying he understands the public must be infuriated “to think that the people who are setting the rules have not been following the rules”.

That came as he announced new restrictions to stop the spread of the virus. They include:

• Everyone who can work from home must do so from Monday;
• Mandatory masks will be extended to most public venues, including theatres and cinemas;
• Proof of vaccination will be mandatory for entry into nightclubs and venues where larger crowds gather.

“You’ve got to act to protect public health when you have got the clear evidence,” Mr Johnson said in response to suggestions that the Plan B rules announcement was timed as a diversion from questions over his team’s Christmas party.

On Wednesday, video surfaced of staffers work-shopping how to answer questions if they was asked about the party.

Allegra Stratton, who was most recently Mr Johnson’s COP26 spokeswoman, was his press secretary at the time the video was recorded in December 2020.

In the video aired by ITV, Ms Stratton was shown at a rehearsal for a daily briefing laughing and joking about a reported gathering at a time when tens of millions of people across the UK were banned from meeting family and friends to celebrate Christmas, or even from bidding farewell to dying relatives.

A teary Ms Stratton met with reporters outside her home on Thursday morning to publicly announce she would step down.

“My remarks seemed to make light of the rules, rules that people were doing everything to obey. That was never my intention. I will regret those remarks for the rest of my days,” she said.

“I understand the anger and frustration that people feel. To all of you who lost loved ones, who endured intolerable loneliness and who struggled with your businesses – I am truly sorry and this afternoon I am offering my resignation to the prime minister.”

Tweet from @SkyNews

Mr Johnson said he had been furious to see the clip and that, since allegations emerged in the media, he had been repeatedly assured that there had not been a party.

“I apologise unreservedly for the offence that it has caused up and down the country and I apologise for the impression that it gives,” he told parliament, adding that there would be disciplinary action if it was found rules were broken.

Mr Johnson and his ministers have repeatedly denied any rules were broken by the gatherings in late 2020 although the Mirror newspaper said Mr Johnson spoke at a leaving party and that his team had a wine-fuelled gathering of about 40 to 50 people.

But the video of Ms Stratton suggests Mr Johnson’s team rehearsed how to answer questions about the party.

In the video, adviser Ed Oldfield asks Ms Stratton a question she might face from the press: “I’ve just seen reports on Twitter that there was a Downing Street Christmas party on Friday night – do you recognise those reports?”

Ms Stratton, standing before UK flags at an official Downing Street lectern, laughs and says: “I went home.”

“Hold on. Hold on. Um, er, arh,” she says, appearing lost for words.

One of the staffers then suggests she call it “cheese and wine”.

“Is cheese and wine alright?,” she says, and they all laugh.

“This fictional party was a business meeting…and it was not socially distanced,” Ms Stratton says.

Tweet from @Mukhtar_iam

Reaction to the video was sharp with many people on Twitter expressing disgust that Downing Street appeared to be laughing about breaking rules.

Some questioned whether or not the public should obey Mr Johnson if he imposes more COVID-19 restrictions.

Nearly 146,000 people have died from COVID-19 in the United Kingdom and Johnson is weighing up whether to toughen curbs after the discovery of the new Omicron coronavirus variant.

Mr Johnson has faced intense criticism in recent months over his handling of a sleaze scandal, the awarding of lucrative COVID-19 contracts, the refurbishment of his Downing Street flat and a claim he sought to ensure pets were evacuated from Afghanistan during the chaotic withdrawal of foreign forces.

Opposition Labour Party leader Keir Starmer said the video was an insult to those who had followed lockdown rules when it meant being separated from their families over Christmas.

“They had a right to expect that the government was doing the same. To lie and to laugh about those lies is shameful,” Mr Starmer said in a statement.

“The prime minister now needs to come clean and apologise.”

Ian Blackford of the Scottish National Party, the second-biggest opposition party in parliament, called for Mr Johnson to step down.

Conservative Party MP Roger Gale said that if the House of Commons had been deliberately misled over the party then it would be a resignation matter.