Boris Johnson is gambling on an unprecedented ramping up of vaccinations, rolling out 1m booster jabs a day to stem an incoming “tidal wave of Omicron” and avoid imposing further restrictions.

The army will be deployed across the country to help rapidly accelerate the vaccine programme and GPs will be told to cancel appointments to dedicate resources to offering vaccines to every UK adult by the end of December.

In a televised address to the nation on Sunday night, the prime minister said he was “afraid we are now facing an emergency in our battle with the new variant, Omicron, and we must urgently reinforce our wall of vaccine protection to keep our friends and loved ones safe.”

Johnson, who is facing a major test of his authority this week as MPs rebel against new Covid restrictions, called the target “a national mission unlike anything we have done before in the vaccination programme”.

It means vaccinating around 1 million people a day, up from 530,000 on Saturday. The UK record is 844,000 in March. All over-18s will be eligible from Monday, and NHS booking will open to that age group from Wednesday. Until now eligibility has been limited to over-40s.

Jabs will be available on Christmas Day, though demand is expected to be low.

On Sunday the Covid alert level was raised from 3 to 4, indicating substantial pressure on the NHS, after a further 1,239 UK cases of Omicron were confirmed, nearly double the number reported the previous day. Omicron is expected to become Britain’s dominant variant within days, and Johnson warned it could “overwhelm the NHS and lead to very many deaths”.

Announcing the booster offensive, Johnson said: “We know from bitter experience how these exponential curves develop. No one should be in any doubt: there is a tidal wave of Omicron coming.” He said two doses of vaccine were not enough, but scientists were confident that three would make a huge difference.

On Friday UK data suggested that three jabs provide 70-75% protection against infection with Omicron, while two doses given three or more months ago give 30% to 40% or less.

GPs and other vaccinators will be required to prioritise jabs over non-urgent care and reduce the number of other face-to-face interactions. Johnson will also scrap the 15-minute post-jab wait in order to speed through even greater numbers of people.

Forty-two military planning teams will be deployed across every region of the UK, and there will be additional vaccine sites and mobile units. There will be extended opening hours with more appointments early in the morning, in the evening and at weekends, and thousands more volunteer vaccinators will be trained.

Hospitals expect NHS England to declare a national incident within days, the Guardian has learned, making decision-making more centralised and likely leading to routine operations being cancelled with staff redirected.

The prime minister said it could not be taken for granted that Omicron was causing less severe illness. “Do not make the mistake of thinking Omicron can’t hurt you, can’t make you and your loved ones seriously ill,” he said.

Johnson is facing open war in the Tory party over the move to plan B restrictions, with the biggest rebellion since his election expected from MPs opposed to Covid passports for large venues and more mask wearing.

Up to 100 MPs could oppose the changes on Tuesday as Johnson battles on multiple fronts to contain the damage from reports of a series of parties in Downing Street last year, which have left MPs openly discussing a vote of no confidence.

The acceleration of the booster rollout, which will put Johnson under pressure to meet the target, is likely to be a key argument to reassure furious Tory MPs who have warned the prime minister they will not tolerate further restrictions.

Johnson will offer a number of concessions to the rebels, starting with an announcement that from Tuesday contacts of Covid cases will be able to take a lateral flow test every day instead of isolating if they have been vaccinated.

The Guardian understands that the red list for travel is likely to be scrapped in the coming days, given the worldwide spread of Omicron. The change would mean there is likely to be no enforced hotel quarantine for people returning from southern Africa, though travellers may be required to isolate at home.

Scientists warned that while booster jabs were crucial, they should be combined with restrictions on the size of gatherings. Prof Christina Pagel, of University College London, said some current policies appeared contradictory, including letting vaccinated people take tests instead of isolating after contact with a Covid case.

“Don’t go to work but go to parties. Get a booster, but it’s fine not to isolate if you’re vaccinated. It’s not consistent,” she said. “This idea that kids can go to school if someone in their house has Covid is just stupid. We should be saying no parties, no gatherings bigger than 10 people, say. We need to think about moving back down the roadmap and restricting contact.”

She added: “I just don’t think they [ministers] can say ‘this is it’ until Christmas when things are so uncertain.”