Dr Chaand Nagpaul, chairman of the council at the British Medical Association, told Sky News: "What's concerning is that we are seeing significant increases in people in hospital.

"In fact, as of yesterday, the number of people admitted and also the number of patients in hospital is at a level as high as during the lockdown earlier this year in spring, in February-March.

"Now that is a significant number and it is increasing, so while the proportion of people who end up in hospital as a result of Omicron is smaller, we are definitely seeing significant increases."

Dr Nagpaul said 25,000 patients were admitted with COVID-19 in the four-week period leading up to Christmas and he said those admissions have been preventing six million people on the NHS waiting list from being treated.

Asked whether those admissions were people taken to hospital because of coronavirus, or for other health reasons and "happened to have COVID", Dr Nagpaul replied: "That's a very good question and, in fact, that's data I don't have and data it is really important is made available, because I absolutely agree, we need to differentiate between the two."

Fresh NHS figures on hospitalisations in England are due to be published today.

Northampton General Hospital became the latest to suspend visitors on Friday, apart from in limited circumstances, amid concerns about rising COVID cases.

In a series of Twitter posts, the hospital confirmed the move and apologised "for having to take this step as we are fully aware of the impact suspending visiting has on our patients and those close to them".

The hospital promised to put virtual visiting facilities in place.

Bath Royal United Hospital and Great Western Hospital in Swindon have also this week suspended visitors, apart from in exceptional circumstances, due to increasing coronavirus infections.

In total, more than a dozen hospitals across the country have temporarily banned visits in efforts to protect patients and staff.

There were also further signs of a squeeze on the NHS workforce due to COVID.

New figures from NHS England showed a total of 4,580 NHS staff at hospital trusts in London were absent for coronavirus reasons on Boxing Day, up 18% on the previous week (3,874) and nearly four times the number at the start of the month (1,174).

The number reached as high as 5,994 on 23 December. The total includes staff who were ill with coronavirus or who were having to self-isolate.

Across England as a whole, 24,632 NHS staff at hospital trusts were absent due to COVID reasons on 26 December, up 31% from 18,829 a week earlier and nearly double the number at the start of the month (12,508).

As the UK gears up for New Year's celebrations tonight - with parties allowed in England, but restrictions on gatherings in both Wales and Scotland - accessing lateral flow and PCR tests continues to be difficult.

A shortage of lateral flow tests means those wishing to mix with others at nightclubs, pubs and house parties face doing so without knowing if they are COVID positive.

Lateral flow tests are available to order on the government portal, but could take days to arrive and Health Secretary Sajid Javid yesterday warned that supplies may need to be "constrained" further because of demand.

PCR tests are available to book on the government's website, but results usually take around 24 hours.

Some in Scotland and Wales are planning to cross the border to England in order to avoid the stricter COVID rules in their countries as they celebrate New Year.

Mark Jones, the landlord at Stanton House Inn in Chirk, Wales, which is less than a mile from the English border, told Sky News that some of his regular customers have booked minibuses in order to celebrate in England.

And Margaret Straughan, landlady of the Brewers Arms in Berwick-upon-Tweed, 1.5 miles from the Scottish border in Northumberland, predicted a "very busy" evening with some of her customers coming from Scotland.

A leading scientist has urged people to take care on New Year's Eve, warning that the Omicron variant "has ended up being so infectious that it almost needs just a whiff of infected breath and you could get infected".

Professor Peter Openshaw, who sits on the New and Emerging Respiratory Virus Threats Advisory Group (NERVTAG), told the BBC: "We're lucky really that it wasn't this infectious when it first moved into human-to-human transmission."

And the head of NHS Providers has warned that even if the government brings in extra restrictions in England, it will take two weeks to reduce the hospital admission rate.

As eight hospital trusts set up new Nightingale "surge hubs" in preparation for an influx of COVID patients, Chris Hopson told Radio 4's Today programme that "we still don't know if a surge will come, and indeed we are exactly talking about the preparations we are making for that surge right now".

He added: "It is worth remembering that it does take about a fortnight for any new restrictions to affect the level of hospital admissions, so the pattern of hospital admissions for the next fortnight has already been set."