Sir Jeremy Farrar - part of the Scientific Advisory Group for Emergencies (SAGE) that has been making recommendations to ministers throughout the COVID-19 crisis - offered a stark warning as the government considers what action to take amid a significant rise in infections in northern England.
His intervention came as an Imperial College and Ipsos MORI study - of 175,000 volunteers across England, and the largest in the country - showed:
- One in 170 people in England had coronavirus between 18 September and 5 October, with 45,000 new infections every day
- One in 100 people had the virus in the North West, which had the highest regional prevalance, followed by the North East (0.9% of people)
- Coronavirus cases are doubling about twice as fast in the North West, Yorkshire and the West Midlands as for the whole of England
Imperial College's Professor Steven Riley, who led the study, warned if the patterns they found didn't change, then "in a relatively short period of time" the country could again reach infection rates comparable to the peak of the infection earlier this year.
He said the data supported further restrictions in the north of England "sooner rather than later".
Sir Jeremy also called for immediate action "to avoid spiralling out of control", as he commented on warnings from local health chiefs that some hospitals in northern England could reach maximum capacity in as little as a week or two.
"We are close to or at events & choices of 13-23 March," he added, referring to Prime Minister Boris Johnson's decision to order Britons to "stay at home" on 23 March.
Urging ministers to implement a "package of interventions now", Sir Jeremy added on Twitter: "We are back to choices faced in the early March.
"With the lag time between making a decision, its implementation & its effect measured in weeks the longer the decisions are delayed the harder & more draconian are the interventions needed to change trajectory of epidemic curve.
"Don't act slower than the speed of the epidemic, don't get behind an epidemic curve.
"So much harder to turn that epidemic curve around."
Sir Jeremy, who is director of the Wellcome Trust medical research foundation, last month called for more COVID-19 restrictions and claimed a previous "slow response in February left us quickly and dangerously behind the curve".
The prime minister is expected to carve England into three different lockdown tiers next week, with millions of people facing tougher restrictions.
Pubs, restaurants and leisure facilities are expected to be closed in those parts of northern England put into the highest tier.
Professor Chris Whitty, England's chief medical officer, on Thursday discussed the rise in infections with MPs from the North and the Midlands.
The MPs were shown data of coronavirus cases and hospital admissions continuing to rise in the North West, North East and Yorkshire.
The MPs were also shown analysis to suggest pubs, bars, restaurants and cafes counted for around 30% of exposure to COVID-19.
However, one unnamed MP quoted by the Daily Telegraph accused the government of having "cobbled together" the data to justify a decision to close pubs.
The newspaper also reported MPs referring to it as a "dodgy dossier".
Mark Spencer, the Conservative chief whip, on Friday confirmed the government is planning to give MPs a vote on new restrictions next week.
"There will be a statement to parliament next week and these things will come into force next week, subject to parliamentary vote of course," he told BBC Radio Nottingham.
"Because you'll recall a fortnight ago there was quite a furore about parliament having its say and MPs wanting to comment on these things before they came into law.
"And that's what we've decided to do, that's what the process is now in place.
"MPs will get to discuss and vote upon these new systems next week, I hope, and then we'll be able to move forward."