The Government is under increasing pressure to up the capacity of coronavirus testing as case levels reached their highest level yet.
A new record was set for the daily number of coronavirus cases on Wednesday, as all four UK nations reported their figures for the first time since Christmas Eve.
But at times on the same day, there were no PCR of lateral flow tests available to order online.
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.
But Health Secretary Sajid Javid admitted there were global supply issues to a senior Tory MP.
Sir Roger Gale told the PA news agency that Mr Javid had confessed there was 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”.
Leyla Hannbeck, chief executive of the Association of Independent Multiple Pharmacies, said people are often unable to find Covid-19 tests in chemists because of “patchy” and “inconsistent” supplies.
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.
Work on a total of eight hubs, each with a capacity of around 100 patients, is set to begin as early as this week, according to NHS England.
Further sites could also be identified to add a further 4,000 “super surge” beds.
The move comes as hospitals are 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.
NHS national medical director Professor Stephen Powis said: “Given the high level of Covid-19 infections and increasing hospital admissions, the NHS is now on a war footing.”
The Government website showed no PCR tests were available at times on Wednesday 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.
The Prime Minister earlier urged people to get swabbed before enjoying new year celebrations.
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.
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.
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.”