The NHS is facing significant pressure as it copes with the latest wave of Covid-19 despite hopes that cases should start to drop in the coming weeks.

Boris Johnson will lead a Downing Street press conference as No 10 admitted that the health service is facing a “difficult time” during a “challenging winter”.

Officials in Whitehall are keeping an “extremely close eye” on hospital capacity, with admissions and occupancy “increasing significantly”.

But the Prime Minister’s official spokesman said: “We’re not seeing that same jump in beds requiring ventilation, which is pleasing, and almost certainly a function of both the nature of Omicron and our successful booster programme.”

He added that the vaccinations and “evidence that Omicron may be milder” means “we are not seeing those huge waves in cases translate into those needing the most serious care that we saw perhaps in previous waves, but that still puts the NHS under significant pressure”.

The latest NHS England figures show 14,210 patients with Covid-19 were in hospital on January 3, including 777 requiring mechanical ventilation.

Downing Street insisted the Plan B measures in place in England remain the right approach despite tougher restrictions in other parts of the UK.

That optimism may be helped by comments from Professor Neil Ferguson, from Imperial College London, whose data was instrumental to the UK going into lockdown in March 2020, who said infection rates may already be plateauing in London and could fall across the country within weeks.

Prof Ferguson, a member of the Government’s Sage scientific advisory panel, told BBC Radio 4’s Today programme: “I would say that, with an epidemic which has been spreading so quickly and reaching such high numbers, it can’t sustain those numbers forever, so we would expect to see case numbers start to come down in the next week, maybe already coming down in London, but in other regions a week to three weeks.

“Whether they then drop precipitously, or we see a pattern a bit like we saw with Delta back in July of an initial drop and then quite a high plateau, remains to be seen.

“It’s just too difficult to interpret current mixing trends and what the effect of opening schools again will be.”

Prof Ferguson said the Omicron variant had not had much time to infect pupils before schools shut for the Christmas break, and a rise in cases is now expected.

Meanwhile, Professor Sir Andrew Pollard, director of the Oxford Vaccine Group, told Sky News it would not be “affordable, sustainable or deliverable” to give regular jabs every six months to cope with waning immunity and the rise of new variants.

“Remember that, today, less than 10% of people in low-income countries have even had their first dose, so the whole idea of regular fourth doses globally is just not sensible,” he said.

Sir Andrew said it may be that future boosters could be targeted at the most vulnerable and it is too early to say whether updated vaccines will be required every year, as with flu.

Downing Street said ministers will also be taking clinical advice and keeping a “very close eye on” the “waning efficacy of second doses and the interplay of Omicron on that as well” as part of a review on whether to make a booster jab a requirement to access a Covid pass.

Elsewhere, Matthew Taylor, chief executive of the NHS Confederation, said the staffing situation in hospitals is “almost impossible” as leaders try to manage their resources.

He told Times Radio that, for many, “the most pressing element of all” is the number of staff who are absent due to Covid.

He added that hospital admissions seem to have “perhaps plateaued in London or there may be a second peak after the new year now, but it’s rising across the rest of Britain”.

Meanwhile, Chris Hopson, chief executive of NHS Providers, said at least “half a dozen” NHS hospitals have declared a critical incident as they try to respond to Covid.

However, the health leader said fears raised before Christmas of a huge rise in the number of seriously ill older people needing critical care and mechanical ventilation has not yet occurred.

“There are a number of chief executives who are saying, if we were going to see that surge, we probably would have seen the beginnings of it up to now, so there are glimmers of hope,” he said.

Morecambe Bay NHS Trust declared a critical incident on Monday evening amid rising Covid hospital admissions and staff testing positive for coronavirus.

Dr Sakthi Karunanithi, public health director for Lancashire County Council, told Today: “Lancashire is beginning to experience what London did at the beginning of last month and, of course, London is better resourced and the infrastructures are well organised compared to other regions, so we are bracing ourselves for a tsunami of Omicron cases in Lancashire.”