Huge queues are forming outside vaccination centres as Brits scramble to get their booster jabs as the new rollout gets off to a chaotic start.
Boris Johnson announced an accelerated booster rollout plan on Sunday, however it has already run into trouble after the NHS website crashed.
An error message came up on the site on Sunday and Monday, stopping people from booking their jabs because of 'technical difficulties'.
Meanwhile, Brits were left unable to order lateral flow tests online as the gov.uk said none were available.
People trying to book their booster on Monday were met with a holding page saying the site is 'currently experiencing technical difficulties'.
The crash comes after Boris 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.
Just hours after Mr Johnson's announcement Brits struggled to schedule their boosters after encountering an error message on the NHS website.
The website was still down on Monday morning, showing the same 'technical difficulties' message.
Brits who managed to get through to the website found themselves in a queue to book their appointment.
On Sunday, Mr Johnson told the nation it was facing an "emergency in our battle with the new variant" and two jabs will not offer enough protection.
But frustrated Brits have been unable to book their jabs after the NHS website crashed.
On Monday morning, one Twitter user said: "NHS covid website is down . Bad gateway when trying to book at jab, just crashing since last night, so can't book jabs."
Another social media user added: "Impossible to book a booster jab appointment at the moment online NHS website keeps crashing."
Someone else posted: "The idiot in charge is useless, he cannot even get this right. Let's announce an accelerated booster program and then let the NHS website crash because they have not put in enough capacity."
It comes after the NHS extended its booster jab programme to those aged between 30 and 39 from Monday.
Health bosses said they are working to resolve the website issues and thanked people for their patience in a message to users.
On Sunday, the UK's Covid alert level raised to its second highest due to the spread of the Omicron variant.
Top medics recommended to ministers that the UK be moved from Level 3 to Level 4 warning that the new strain "adds additional and rapidly increasing risk to the public and healthcare services."
Mr Johnson urged that the strain could rip through an un-boosted population, overwhelming the NHS and leading to "very many deaths".
He said scientists had discovered that two doses of a vaccine is "simply not enough" to prevent the spread of the new variant.
Announcing the new target to vaccinate all adults in England by the new year, he added that we must "urgently reinforce our wall of vaccine protection."
The NHS will postpone some planned appointments in order to meet the target.
NHS England said GP teams will be asked to "clinically prioritise their services to free up maximal capacity" to support the vaccination programme, alongside delivering critical appointments such as cancer, urgent and emergency care.
Nursing leaders have expressed concern about the "scale and pace" of the vaccine programme expansion - which will aim to jab almost a million people every day.
And a charity said the Government must ensure NHS cancer services are "prioritised and protected".
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."
Despite this, she said nursing staff have already played a leading role in the delivery of vaccines and stand ready to do the same again.
The target for giving every adult a booster jab was brought forward by a month over fears of a "tidal wave of Omicron" that could cause "very many deaths".
The mission to administer millions more jabs by December 31 will see 42 military planning teams deployed across every health region.
Extra vaccine sites will be opened and additional mobile units deployed, clinic opening hours are to be extended to allow people to be jabbed around the clock and at weekends, while thousands more vaccinators will be trained.
Get all the latest news sent to your inbox. Sign up for the free Mirror newsletter
An additional 1,239 Omicron cases were reported in the UK on Sunday, nearly doubling the previous daily high.
It takes the total number of infections of the variant to 3,137, including 2,953 in England, 159 in Scotland, 15 in Wales and 10 in Northern Ireland.
Overall, the UK recorded 48,854 new Covid cases and 52 deaths with infections rising 22% in a week, according to government figures.
