A new record has been set for the daily number of coronavirus cases, as all four UK nations reported their figures for the first time since Christmas Eve.
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.
It comes as Boris Johnson’s Government is scrambling to secure supplies of Covid-19 tests.
The Prime Minister earlier urged people to get swabbed before enjoying New Year celebrations.
Ministers acknowledged a worldwide supply issue is hitting the UK, as people again struggled to get tests through pharmacies or delivered to their home.
Health Secretary Sajid Javid set out the issues in a call with a Tory MP, acknowledging there is not a quick fix to a problem caused by global demand.
Leyla Hannbeck, chief executive of the Association of Independent Multiple Pharmacies, has said people are often unable to find Covid-19 tests in chemists because of “patchy” and “inconsistent” supplies.
The Government website showed no PCR tests were available for home delivery, even for essential workers, in England or Northern Ireland, with “very few” in Scotland, while Wales had availability only in some regions.
Home delivery slots for lateral flow tests were also unavailable on Wednesday.
Testing expert Professor Alan McNally said health and key workers should be prioritised for PCR tests as “this is impacting on many many levels now and we really do have to think about how we use our testing capacity to maximise its benefit”.
Prof McNally, director of the Institute of Microbiology and Infection at Birmingham University, was asked on BBC Radio 4’s PM programme whether it was necessary to “double check” a lateral flow result with a PCR test.
He said: “The data is strong enough now for the Government to really reconsider that messaging, and that if you’re positive by lateral flow you have Covid, and therefore do we need to use tens or hundreds of thousands of PCR tests to confirm the results of lateral flow tests?
“To be clear, the guidance at the moment is still that you should get a confirmatory PCR test; what I’m suggesting is that I would really like to see a Government rethink on that.”
Officials acknowledged that during periods of exceptional demand there could be “temporary pauses” in ordering or receiving tests, in an attempt to manage distribution across the system.
The reduced postal system over Christmas has also added to the issues.
In Scotland, First Minister Nicola Sturgeon said testing will be prioritised for essential workers as sampling processing capacity is “under pressure”.
The UK Health Security Agency (UKHSA) is understood to temporarily pause the booking portal to limit the flow of tests into laboratories when there is “exceptionally high demand”.
Tory MP Sir Roger Gale told the PA news agency that Mr Javid had admitted there is a problem with supplies – previously ministers and officials had insisted they had sufficient stocks but the problems were in delivering them to people’s homes or pharmacies.
The North Thanet MP said: “Saj was very honest with me, he said, ‘look, there isn’t a quick fix’.”
Sir Roger said “we have created the demand in England which we now can’t satisfy” as a result.
He added: “The Prime Minister has now found himself caught between the Covid Recovery Group and supporters and the scientists.
“We are now facing the situation where No 10 is saying go and get tested and the Department of Health is saying we haven’t got the tests, we can’t do it.”
He said Mr Javid is “busting a gut” to get supplies “but we’re competing with a global market”.
During a visit to a vaccination centre in Milton Keynes on Wednesday, Mr Johnson urged people to get tested before New Year’s Eve festivities.
He told reporters: “Everybody should enjoy New Year but in a cautious and sensible way – take a test, ventilation, think about others but, above all, get a booster.”
Shadow health secretary Wes Streeting said: “People are trying to do the right thing, follow the Government’s own advice, and test themselves regularly, but are prevented by the Conservative Government’s incompetence.”
The Government said a further 57 people had died within 28 days of testing positive for Covid-19.
Separate figures published by the Office for National Statistics show there have been 173,000 deaths registered in the UK where Covid-19 was mentioned on the death certificate.
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.
This is 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.
NHS colleagues and volunteers will be delivering life-saving booster jabs before the New Year. There are more than one million appointments available between now and 1 January.
Two doses does not give the protection we need from Omicron, #GetBoostedNow. https://t.co/ocH1SqGFXG pic.twitter.com/IfGHiebyba
— NHS England and NHS Improvement (@NHSEngland) December 29, 2021
A UKHSA spokesman 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.”
Meanwhile, Mr Johnson continued to drive forward the Covid-19 vaccination programme, saying he “cannot stress too much” how important a booster shot is.
Congratulations to Boris Johnson who has managed to appear on television today urging people to get tested when people are struggling to access them. Boosting demand without supply. Spectacular incompetence.
— Wes Streeting MP (@wesstreeting) December 29, 2021
Mr Johnson said 2.4 million eligible double-jabbed people are yet to take up the offer of a booster.
He added: “I’m sorry to say this but the overwhelming majority of people who are currently ending up in intensive care in our hospitals are people who are not boosted.
“I’ve talked to doctors who say the numbers are running up to 90% of people in intensive care who are not boosted.”
There are no official NHS figures on the vaccination status of people in intensive care but medics have said the vast majority are either unvaccinated or have not had all their doses.