The insurance firm Aviva, which employs around 5,000 staff in Norwich, is among many businesses introducing guidelines for office Christmas parties, to guard against the spread of the Omicron variant.

The company is asking workers to take a Covid test on the morning of their celebrations, and is advising people to wear masks.

"We're very aware that, as we head into December, people's thoughts turn to festive celebrations," a spokesman said. "Events can continue, but we are asking colleagues to take a lateral flow test on the morning of the event, and wear face coverings as appropriate."

Many large firms are also restricting their work parties to 'team' events, to restrict their size and limit the potential for spreading Covid.

The government has said there is no need to cancel Christmas parties, despite the emergence of the Omicron variant. However, many businesses and staff are already changing their plans.

According to a survey of 2,000 office workers commissioned by Covid testing company Prenetics, about 52% of UK workplaces have decided not to hold a Christmas office party this year.

Meanwhile, George Freeman, the Mid Norfolk MP and business minister, said it was a matter for individual companies, but that larger firms might want to consider cancelling festive gatherings.

He told BBC Radio 4's Today programme: "Individual businesses, in the end, have to make judgments on what is appropriate internally.

"It slightly depends on the nature of the business. For many small businesses, four or five staff, who are working together every day anyway, gathering to have a drink isn't a big step up in risk.

"But some companies might normally bring hundreds of people in from around the world to a big party, and they may decide, this year, is that sensible given the pandemic and given where we are?

"In the end, I think business people know how to make those decisions. The government has set out clear guidance."

In an interview with LBC Radio, Mr Freeman said he was cancelling his own staff party this year.

There has been a "sharp series of cancellations" in Christmas parties since the emergence of the Omicron variant, according to the executive chairman of a major ad agency.

Sir Martin Sorrell, of S4Capital, said there is "extreme" uncertainty.

Asked if they were cancelling office parties, he told the BBC Radio Four Today programme: "It's not so much what we're doing as what we see our clients doing and other people.

"The answer is they are doing that, they are cancelling, (there has) been quite a sharp series of cancellations since this happened just, what, three, four, five days ago.

"We have been through this before with Delta and the previous variants, so you would have thought the Government would be a little bit more prepared for what may or may not happen in terms of scenario planning."