Now is not the right time to trigger Plan B against rising Covid infections, a health minister has insisted, as a leading virologist said the UK is probably already close to 100,000 cases per day.

Edward Argar said the Government thinks people should still be able to make their own “educated judgments” when it comes to issues such as wearing face masks, adding that Plan A for tackling the virus “is still working”.

He said ministers will not hesitate to bring in further measures if and when they are needed, although the view at the moment is that the pressure on the NHS is at a “sustainable” level.

It came as leading virologist Dr Chris Smith said the UK is probably already close to 100,000 cases a day, while Professor Adam Finn said it is wrong to see the current death toll as acceptable.

Dr Smith, from the University of Cambridge, told BBC Breakfast that around half of Covid cases are asymptomatic.

“So probably, with detected cases at 50,000, we’re probably already close to 100,000 cases a day anyway, we just don’t know about lots of them,” he said.

“We are looking very hard, we’re doing more than a million tests a day now, but probably we do have really high levels bordering on that sort of number at the moment.”

Dr Smith added: “The trend at the moment in cases is upwards, but the more reassuring trend for the moment is how many people are becoming severely unwell, how many people are losing their lives and that number, thankfully, does remain very, very low, and that’s a direct testimony to the performance of the vaccines.”

Prof Finn, an expert in paediatrics, said five million adults, mostly young adults, who have not had their vaccination should now come forward.

He told LBC radio: “It’s the responsibility of adults to look after children by getting vaccinated and stopping spreading this virus around because there’s a lot more adults infecting children than there are children infecting adults.”

Asked if 100,000 cases a day should be seen as petrifying (a figure that Health Secretary Sajid Javid has twice said could be reached), Prof Finn said: “Yes, it absolutely should.

“I mean we’re being told that somehow it’s OK because there’s only 150 to 200 deaths a day.

“Well, in two weeks, that’s the same number of people who died in the 9/11 attacks in the USA and that was enough to start global wars.

“It really isn’t OK to have this many people getting this infection and getting sick and dying. It’s a real big deal.

“And on top of all of the other struggles that we’ve got in the NHS, we really all need to be doing everything we can to bring these cases back down again, as indeed is happening in other European countries that are our neighbours.

“We just need to look across the Channel to the French to see how we should be behaving.”

For now, ministers have rejected further control measures from Plan B, including vaccine passports for indoor events and the return of mandatory face coverings.

On Wednesday evening, Mr Javid urged the public to play its part, saying further restrictions may be needed if people do not take care and get all their Covid jabs and boosters.

Speaking on Sky News, Mr Argar defended the Government’s position, adding: “While under huge pressure at the moment, and I pay tribute to all those working in it (the NHS), it is a sustainable pressure at the moment.”

Asked how bad the situation in the NHS will have to get before the Government moves to Plan B, he said it would not “be appropriate to set an arbitrary figure, X number of infections, X number of hospitalisations”.

He added: “We need to look at all this in the round, we need to look at the death rate, absolutely.

“We need to look at that booster rollout programme … vaccination programme … vaccination rates in young people, the 12 to 15-year-olds, because we’re seeing in that school-age population, that’s where we’re seeing actually the biggest increases driving these infections.”

He added: “I can’t give you a simple… here is a sort of black and white answer, here is a binary line, because it takes … there’s a whole range of factors we’ll take into consideration.”

Later, on Times Radio, he said bed occupancy is one measure being kept under review, and, while about 7,000 beds are currently occupied by Covid patients, about 6,000 are unoccupied.

He added: “We do have a degree of headroom at this time, we continue to monitor it hour by hour, day by day, to see what’s happening with those figures, both in terms of infection, but also crucially in terms of hospitalisation.

“Our assessment at the moment is the most effective way to continue to control that is for people to get those booster jabs.”

Downing Street flatly denied that ministers or officials are considering a Plan C to ban household mixing in order to control coronavirus this winter.

The Prime Minister’s official spokesman said: “I’ve seen the reporting this morning about household mixing – it’s important to stress that neither ministers nor officials are working on these proposals. That is not accurate.”

It came as the NHS sought to improve access to booster jabs by opening the national booking service (phone and online) for eligible people who had their second vaccine six months and one week ago.

Charities are among those who have warned that vulnerable people are struggling to access booster jabs, while care leaders suggested the system for giving boosters in care homes is chaotic.