The target for giving every adult in England a booster jab has been brought forward by a month over fears of a “tidal wave of Omicron” that could cause “very many deaths”.

Boris Johnson, in a pre-recorded address to the nation on Sunday evening, said Britain “must urgently reinforce our wall of vaccine protection” as he set a new deadline of jabbing everyone over 18 by the new year.

He said scientists had discovered that being fully vaccinated is “simply not enough” to prevent the spread of the coronavirus mutation and that, without a lightning speed mass booster campaign, the NHS could be overwhelmed.

Read more: UK Covid alert level raised following surge in Omicron cases

The mission to administer millions of jabs by December 31 will see 42 military planning teams deployed across every health region, extra vaccine sites and mobile units, extended clinic opening hours to allow people to be jabbed around the clock and at weekends, and the training of thousands more volunteer vaccinators.

The announcement comes as the UK Covid alert level was raised to Level 4, up from Level 3, following a rapid increase in the number of Omicron cases being recorded.

Read more: More than 500 new coronavirus cases reported across Dorset

The recommendation was made to ministers by the country’s four chief medical officers and NHS England’s national medical director following advice from the UK Health Security Agency (UKHSA).

The UK, as of Sunday, recorded a further 1,239 confirmed cases of the Omicron mutation, bringing the total number of cases to 3,137 – a 65% increase from Saturday’s total of 1,898.

Education Secretary Nadhim Zahawi said the actual number was likely to be 10 times as high.

Speaking on Sunday, the Prime Minister said: “We’ve already seen hospitalisations doubling in a week in South Africa and we have patients with Omicron here in the UK right now.

Read more: Daily rapid testing for double-jabbed Covid-19 contacts in England from Tuesday

“At this point our scientists cannot say that Omicron is less severe.

“And even if that proved to be true we already know it is so much more transmissible that a wave of Omicron through a population that was not boosted would risk a level of hospitalisation that could overwhelm our NHS and lead sadly to very many deaths.

“So we must act now. Today we are launching the Omicron emergency booster national mission, unlike anything we’ve done before in the vaccination programme, to get boosted now.

“A fortnight ago I said we would offer every eligible adult a booster by the end of January.

“Today in light of this Omicron emergency I’m bringing that target forward by a whole month.

“Everyone eligible aged 18 and over in England will have the chance to get their booster before the new year.”

The Prime Minister – whose address was pre-recorded, meaning he spoke to the nation without being flanked by his scientific advisers and without taking questions – said the UK Government would support the devolved administrations to “accelerate” their own rollouts of third jabs.

He revealed that the decision to speed up the jab rate would mean some NHS appointments would need to be postponed until the new year, arguing there would be “even greater” cancellations if the Omicron wave was allowed to rise.

In a direct plea to GPs, doctors, nurses and others on the NHS front line who he said had “worked incredibly hard” throughout the pandemic, Mr Johnson said: “I must ask you to make another extraordinary effort now, so we can protect you, and your colleagues, and above all protect your patients from even greater pressures next year.”

Every adult over 18 in England who has had a second dose of a vaccine at least three months ago will be able to have their booster starting on Monday, the Conservative Party leader added.

The NHS booking system will be open for those under the age of 30 from Wednesday but “in some cases you can walk in from tomorrow”.