Face masks and other Covid restrictions could be reintroduced in England in as little as three weeks if hospital admissions rise above anticipated levels, scientists advising the government have warned.

Members of the Scientific Advisory Group for Emergencies (Sage) have reportedly said Boris Johnson should be ready to take action in the first week of August to avoid the NHS being overwhelmed.

The i reports that if admissions exceed central estimates – that daily hospitalisations in the UK will peak at the end of next month at between 1,000 and 2,000 and daily deaths will reach 100 to 200 – Sage scientists have advised that some measures such as mandatory masks and working from home advice should be reinstated at the beginning of August.

Recent government figures show that in the middle of July – six weeks ahead of the forecasted peak and before removal of England’s coronavirus restrictions on 19 July – the UK had already reached 745 daily hospital admissions and this has continued to rise.

On Monday, there were 4,567 patients in hospital with coronavirus – 611 of whom were on beds with ventilators – and from 8-14 July the figure rose by 38.4%.

On Tuesday, 46,558 new people tested positive and 96 people died – the highest daily death toll in nearly four months.

It comes after England’s chief medical officer, Prof Chris Whitty, last week said hospitalisations were doubling approximately every three weeks and could reach “quite scary” levels within weeks. He also said restrictions may need to be reimposed.

According to this projection, hospital admissions could reach nearly 1,500 daily admissions in the first week of August, peaking at 3,000 by the end of the month, close to that of the first wave in April last year.

Insiders told i there was great uncertainty about the modelling and that the situation would continue to change based on vaccinations and individual behaviour.

Last week, when Johnson confirmed the removal of legal restrictions in England, the prime minister’s spokesperson declined to rule out bringing back some lockdown restrictions. But the prime minister said he wanted to avoid it.

Prof Dominic Harrison, the director of public health for Blackburn with Darwen council, told i: “Any return to non-pharmaceutical interventions (NPIs) to control spread would have to focus on those that give the biggest suppression effect.

“Essentially we might expect a reverse through the lockdown lifting steps with each ‘reverse step’ being introduced to match the scale of the surge in cases.”

The Guardian has approached the Department of Health and Social Care for comment.