It is "very worrying" that a shortage of Covid-19 lateral flow tests could lead to people mixing over the New Year without being able to see whether they are infectious, a leading scientist has said.
According to the government's booking website, there are no lateral flow tests available to order across the UK and many pharmacies have run out of packs.
It comes after much of the UK was hit by intermittent availability of slots at PCR test centres and the option to order them online, with no availability across the UK for much of Thursday.
The lack of Covid tests comes as the UK reported a new record number of cases, as all four nations reported their figures for the first time since Christmas Eve.
Wednesday also saw a lack of availability of tests, with pharmacies voicing concern over demand outstripping supply with chemists running out of lateral flow tests to handover at the counter.
Coronavirus: What you need to know
Professor Peter Openshaw, who sits on the New and Emerging Respiratory Virus Threats Advisory Group (Nervtag), said the shortages were "very worrying".
The scientist warned it could lead to people mixing over the New Year without being able to see whether they are infectious.
"We know the situations in which transmission happens and fortunately I don’t think we are facing the sort of lockdown that was necessary in order to cope in the very earliest part of this year," Prof Openshaw told BBC Radio 4’s Today programme.
"But we do know that crowding together in poorly ventilated spaces, particularly if you are shouting over loud music and so on, is absolutely perfect in terms of transmitting this very, very highly transmissible virus."
Health Secretary Sajid Javid has admitted a global supply issue is impacting the UK and admitted the UK may need to "constrain" supply over the next two weeks as a result.
In a letter to MPs, Mr Javid said the supply of lateral flow tests (LFD) was being tripled in January and February from a pre-Omicron plan of 100 million to 300 million per month.
"To respond to anticipated demand over the coming few weeks we are buying hundreds of millions more LFD tests, bringing new products on board and accelerating their deployment to the public,” he said.
But "in light of the huge demand for LFDs seen over the last three weeks, we expect to need to constrain the system at certain points over the next two weeks to manage supply over the course of each day, with new tranches of supply released regularly throughout each day".
As the shortage continued, the Welsh government said it would loan four million more lateral flow tests to the NHS in England, bringing that mutual aid to a total of 10 million.
First Minister Mark Drakeford said: “Wales has a significant stock of lateral flow tests, sufficient to meet our needs over the weeks ahead.”
Has demand for lateral flow tests gone up?
In short, yes. The government has urged the country to regularly take lateral flow tests - repeating their advice particularly in the run up to Christmas and New Year celebrations.
Official guidance suggests individuals take a test on days when mixing with others indoors, and tells people to swab daily if they've been in contact with someone who has the virus.
The change in isolation rules in England (reducing quarantine time from 10 days to seven for people with Covid) also relies on getting two negative lateral flow results on days six and seven.
There are concerns without access to lateral flow tests key workers, including those in the NHS, will be unable to return to work after seven days of isolation.
On Wednesday, the prime minister urged people to get swabbed before enjoying new year celebrations.
Prime Minister Boris Johnson urged people in England heading out for New Year’s Eve festivities on Friday to get tested, despite the lack of tests available.
'Take a test, ventilation, think about others – but above all, get a booster.'
In England – unlike other parts of the UK – nightclubs remain open and there are no limits on social mixing.
The NHS Covid Pass is required for entry to nightclubs, but this can be obtained by people who are double-jabbed, rather than requiring proof of a negative test.
Labour said "it's absolutely critical people are able to test regularly" and said issues with getting holds of tests was putting "the strategy at risk".
Shadow culture secretary Lucy Powell said: "The lack of access to tests, both lateral flow and PCR, is really putting at risk the strategy for this Christmas and New Year period, and for schools going back in January as well, because it's absolutely critical that people are able to test regularly.
"If they can't have access to tests what are they supposed to do then?" she said.
"It's absolutely critical - the entire system is based on access to testing. It's not like the government couldn't see this coming. They saw it coming with the initial arrival of Omicron a few weeks ago, it was raised in parliament then about access to tests - and the government really should have foreseen this coming and should have been doing a lot more to ensure people had access to tests at this critical juncture."
'The government really should have foreseen this coming'
It comes as the NHS is setting up new Nightingale “surge hubs” at hospitals across England as it goes on a “war footing” to prepare for a potential wave of Omicron hospital admissions.
Hospitals are already using hotels, hospices and care homes to safely discharge as many people who are medically fit to leave as possible – freeing up beds for those who need them most.
The government is under increasing pressure to up the capacity of coronavirus testing as case numbers reached their highest level yet.
The UK government said that a further 183,037 lab-confirmed Covid-19 cases had been recorded in the UK as of 9am on Wednesday.
The total includes reported figures for Northern Ireland covering a five-day period, but the 138,287 figure for England was also the highest recorded.
A total of 10,462 people were in hospital in England with Covid-19 as of 8am on December 29, according to figures from NHS England - up 48% from a week earlier and is the highest number since March 1.
During the second wave of coronavirus, the number peaked at 34,336 on January 18.
A UKHSA spokesperson said: “We are delivering record numbers of lateral flow tests to pharmacies across the country, with almost eight million test kits being made available to pharmacies between today and New Year’s Eve.
“We have made 100,000 more PCR booking slots available per day since mid-December and we are continuing to rapidly expand capacity, with over half a million tests carried out on 23 December alone and delivery capacity doubled to 900,000 PCR and LFD test kits a day.
“If you have not been able to get the test you need from gov.uk, please keep checking every few hours as more PCR and LFD tests become available every day.”