Coronavirus lateral flow tests have run out again for the second day in a row, according to the gov.uk website.
But the government insisted on Monday that there was no shortage of kits as 'ample supplies' exist it shops.
Yet on Tuesday morning a new message on the gov.uk website said 111, 119 and 999 did not have access to any more tests - as well as none being available for home deliveries.
It comes after the launch of Boris Johnson's accelerated Covid booster programme, which saw the NHS vaccine booking website crash on Sunday and Monday.
Huge queues formed outside vaccination centres across the country on Monday as Brits scrambled to get jabbed as part of the national effort to tackle the Omicron variant.
Meanwhile, the online booking system for lateral flow tests has come under strain, with the gov.uk website announcing it was out of kits on Monday and Tuesday.
A message on the site on Tuesday morning said: "There are no rapid lateral flow tests available to order today for home delivery.
"You can still pick up rapid lateral flow tests from a pharmacy or collection point today. Only pick up tests if you do not have symptoms.
"111, 119 and 999 do not have access to more rapid lateral flow tests today."
The UK Health Security Agency has clarified that the warning about 111, 119 and 999 has been put out to ensure people do not ring these numbers to ask for home kits.
It does not mean there is a shortage of lateral flow tests among paramedics, police officers or medical staff.
Boris Johnson reiterated that home test kits were available at pharmacies when he was challenged over the message on the website.
He said: "They can get those tests, we do have a ready supply of lateral flow tests.
"If you can't get one online for any reason, then there are ample supplies in the shops. But what I think, if I may say so, what that also shows is that people are doing the sensible thing, and getting tests as well."
On Monday, the UK Health Security Agency said that "due to exceptionally high demand, ordering lateral flow tests on gov.uk has been temporarily suspended to fulfil existing orders".
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It comes after Mr Johnson urged people to book their third dose to tackle the spread of the Omicron strain.
On Sunday he announced plans to offer jabs to every adult in England by New Year's Eve.
The ambitious programme will aim to jab almost one million people per day for the rest of December.
However nursing leaders and a cancer charity have expressed concerns about the impact this may have on the NHS.
Steven McIntosh, executive director of advocacy and communications at Macmillan Cancer Support, said: "The Government also must not fail to ensure NHS cancer services are prioritised and protected this winter to ensure that nobody faces long waits and disruption in vital cancer care."
Pat Cullen, general secretary and chief executive at the Royal College of Nursing, also raised concerns.
She said: "We are concerned about the scale and pace of this expansion, given these same nurses are already facing huge demands under existing unsustainable pressures in every part of the UK health and care system."
