A prominent adviser to the government on Covid-19 has said he is very fearful of another “lockdown Christmas”, as he urged the public to do everything possible to reduce the spread of the virus.

Prof Peter Openshaw, a member of the New and Emerging Respiratory Virus Threats Advisory Group (Nervtag), said case numbers and death rates were currently unacceptable, and re-emphasised the importance of measures such as working from home and mask wearing as part of efforts to control the spread of Covid.

His intervention comes after the prime minister resisted calls from health leaders, including the head of the NHS Confederation and the council chair of the British Medical Association, who urged “categorically” that the “time is now” for tighter restrictions.

Asked on Friday about the possibility of a winter lockdown, Boris Johnson claimed there was “absolutely nothing to indicate that that is on the cards at all”. The chancellor, Rishi Sunak, also said the vaccine rollout and booster jabs made a lockdown or “very significant economic restrictions” unlikely.

The health secretary, Sajid Javid, conceded earlier this week that new cases could reach a record 100,000 a day, but Downing Street insisted there was still spare capacity in the NHS and that “plan B” winter measures, including mandatory use of face masks and working from home guidance, would only be activated if it came under significant pressure.

Speaking in a personal capacity, Openshaw told BBC Breakfast on Saturday he feared “another lockdown Christmas if we don’t act soon”. He said: “We know that with public health measures the time to act is immediately. There’s no point in delaying. If you do delay then you need to take even more stringent actions later. The immediacy of response is absolutely vital if you’re going to get things under control.”

He said getting measures in place now in order to “get transmission rates right down” was key to having “a wonderful family Christmas where we can all get back together”.

Openshaw said it was “unacceptable to be letting this run at the moment”, adding: “I think the hospitals in many parts of the country are barely coping actually. Talking to people on the frontline, I think it’s just not sustainable to keep going at this rate.”

Last week, the UK recorded its highest number of Covid-related deaths since March.

Openshaw said: “At one stage last week there were 180 deaths in a single day. That is just too many deaths. We seem to have got used to the idea that we’re going to have many, many people dying of Covid and that I think is just not the case,” he said.

He urged the public to take matters into their own hands to slow down transmission of the virus, rather than waiting for the government to reintroduce measures, including avoiding public transport and crowded spaces if possible, getting vaccinated and accepting the offer of the booster jab.

“The sooner we all act, the sooner we can get this transmission rate down, and the greater the prospect of having a Christmas with our families,” Openshaw said.

Experts on the Scientific Advisory Group for Emergencies (Sage) said, in minutes of a meeting published on Friday, that a further huge rise in infections as seen in January was “increasingly unlikely”, as experts predicted a series of broader, flatter peaks as the virus continues to spread.

However, in its meeting dated 14 October, Sage warned measures from the government’s plan B would have greatest effect if brought in in unison and earlier on rather than later.

On Friday, trade union leaders representing 3 million frontline workers attacked the government’s “laissez-faire approach to managing the pandemic”, warning that it risks “another winter of chaos” without urgent action to curb the spread of Covid, including mandatory mask-wearing in shops and on public transport.

And at least a dozen local public health chiefs in England have broken from the government’s official guidance and recommended so-called plan B protective measures, including mask-wearing and working from home, to combat a surge in Covid infections in their areas.