The supermarket chain told Sky News that about 3,300 people were currently at home - representing 11% of its entire workforce - as rules to stem the spread of the COVID-19 Omicron variant add to disruption.

Iceland said the rates of staff absences in recent days were more than double last year's peak during the so-called 'pingdemic' when users of the NHS COVID app, identified as coming into close contact with someone who had tested positive, had to isolate for 10 days.

The company, which had reported "strong sales" in the run-up to Christmas, said it closed two stores on New Year's Day to spread available store workers around.

It spoke up as the wider grocery sector - credited with feeding the nation during lockdown conditions since March 2020 - voiced fears that shoppers could face difficulties if the isolation situation deteriorated.

Helen Dickinson, chief executive of the British Retail Consortium which represents the chains, said: "Staff absences continue to rise in line with rising COVID cases, however the overall situation remains manageable throughout the supply chain.

"Retailers are monitoring the situation closely - clearly, continued rising absence rates due to self-isolation will get increasingly difficult to sustain."

As a growing number of hospitals warn on services, staff absence rates on Britain's railways are running at about one in ten.

An average of about one in 20 services was cancelled over the last fortnight, according to the train firm industry body the Rail Delivery Group.

Guidance which means people should work from home if they can is easing some of the pressure on services.