From tomorrow, everyone over 18 can get their Covid booster vaccination - with the aim of getting everyone jabbed by the end of the year.

The Prime Minister has announced what he has called the "emergency booster national mission".

Boris Johnson addressed the nation in a televised speech at 8pm.

It comes as the UK's Covid alert level has increased from Level 3 to Level 4 in the wake of a rapid rise in cases of the Omicron variant.

In his speech, Mr Johnson said: "Do not make the mistake that Omicron cannot make you and your loved ones seriously ill. Our scientists, at this stage, 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.

"We are launching the Omicron emergency booster national mission, unlike anything we’ve done before in the vaccination programme, to get boosted now."

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.

The national booking service will open up to everyone aged 18 and over from Wednesday but some vaccination sites may offer a walk-in service for 18s and over from tomorrow if they have spare capacity More vaccination centres will be opening and there will be 50 military planning experts brought in to help coordinate the national effort by supporting the NHS with logistics of the rollout.

Over the next week, opening hours for vaccine centres will be extended and every area of the country should have centres available that are open seven days a week.

More pop-up sites will be coming online with local areas looking at the most convenient sites for their communities – from trucks and buses in parks and shopping centres to sports stadiums and leisure centres. Some new sites will go live throughout the week.

Mr Johnson said in order to reach the new jab target, some other medical appointments and elective surgery will need to be postponed to the New Year. And GP teams will be asked to clinically prioritise their services to free up maximal capacity to support the Covid-19 vaccination programme.

NHS staff will also be redeployed so that they can focus on protecting the entire country as quickly as possible and military aid will be in place in every region across the country to support NHS staff with planning for the extra vaccinations.

Amanda Pritchard, NHS chief executive said: “NHS staff were already working incredibly hard to deliver Covid vaccines as swiftly as possible but the threat posed by Omicron is grave.

“Scientists are very concerned about the spread of Omicron due to the speed with which it spreads and because two doses do not appear to provide much protection but thankfully, a booster dramatically improves this.

“That is why the Government have asked us to prioritise boosters over other routine care.

“I know NHS staff will again, do everything in our power to rise to this extraordinary challenge and ensure the covid-19 vaccination programme provides as much protection as possible as we prepare for a new wave of infections that could be even greater than those that have gone before.

“The online booking system is already open to millions of people and will shortly open to all adults – please don’t hesitate with your booking and get boosted now.”

Dr Emily Lawson, director of the NHS Covid-19 vaccination programme said: “The NHS is turbo charging the booster vaccination programme so that as many adults in England as possible can top up their immunity against the virus quickly.

“We know that speed is of the essence and so we will take every opportunity to improve access to the jab, from pop up sites in the community, GP teams doing even more vaccines each day and new sites opening up across the country

“The best way to get your vaccine is by booking online or by calling 119 – please do keep checking availability as we load more appointments onto the system every day.”

There were a further 1,239 confirmed cases of the Omicron mutation recorded in the UK as of Sunday. It brings the total number of UK cases of Omicron to 3,137, a 65% increase from Saturday’s total of 1,898 UK cases.