A leading government adviser has warned the UK is on course for "tens of thousands of deaths" during the current wave of coronavirus.
Prof John Edmunds said the government's current approach would lead to "a high level of incidence everywhere".
But he struck a note of optimism on the prospects of a vaccine in the coming months.
There were about 40,000 deaths in the UK in the first six months of the coronavirus pandemic.
It's difficult to know how the toll of the second wave will compare, but roughly the same number of people are currently in hospital with coronavirus as in March when the UK went into a national lockdown.
England's deputy chief medical officer Jonathan Van-Tam has previously described coming deaths from the infections that have already happened as being "baked in".
Prof Edmunds, an infectious diseases expert at the London School of Hygiene and Tropical Medicine (LSHTM), was addressing a committee of MPs as part of a panel of experts, about lessons learned from the pandemic.
He said no one thought that Tier 3, the toughest restrictions currently being imposed in England, would bring the virus's reproduction rate below one.
An "R number" - the number of extra people infected by each case of the virus - above one means the epidemic is growing; below one and it's shrinking.
"What worries me a little bit is really where this strategy leads to," Prof Edmunds said.
"Let's say Tier 3 works and keeps the reproduction number at about one - and I don't think anybody really thinks it's going to reduce it to less than one - that means that in Liverpool and Manchester and the north west, now we'll keep the incidence at this high level which is putting hospitals under strain."
Any area in a lower tier will see its epidemic keep growing, Prof Edmunds said, until it has to be brought into Tier 3.
Vaccine in 'not too distant future'
But he was more positive about the prospect of a vaccine in the coming months.
"I think it's an almost certainty that we'll have a vaccine that will help us manage this epidemic" in the "not too distant future".
And he said it was "certainly possible" there'd be a vaccine for the highest risk groups by the end of the winter.
At a later session, Dr Clare Gardiner, director of the Joint Biosecurity Centre, said she was looking to develop a set of thresholds as a guide on when areas should be placed into a higher tier.
Her organisation uses evidence to advise on coronavirus alert levels,
Dr Gardiner said this was likely to include case rates, cases in the over-60s, the proportion of all tests coming back positive and the rates of change of each of these metrics.
She gave as an example of "somewhere in the region of" 150 cases per 100,000, a positivity rate of about 7% and a rate of change of about 60% per week.
But she said it was still a "live conversation" about where the thresholds would be set and whether they would be published - although she said she was "supportive" of publishing the criteria.
Test and trace
Prof Edmunds also exchanged words with health and social care select committee chair Jeremy Hunt over the Scientific Advisory Group for Emergencies' (Sage) advice to the government in March.
Mr Hunt asked why Sage did not model test and trace as a national strategy for tackling the pandemic, alongside a lockdown and herd immunity.
Prof Edmunds said a previous paper had been published on test and trace.
But he added that at that point, when there were "perhaps 100,000 to 200,000 infections a day, there is no way that anybody can test and trace their way out of that".
Mr Hunt has previously raised the question of why advisers did not recommend building a contact-tracing system from March.
Dr Matt Roser, founder of Our World in Data, also gave evidence, shedding some light on UK testing figures which are high compared with many other European countries.
He said: "It's not just about the number of tests - this was very much a focus in the UK and I think this was a mistake. It's about testing in proportion to the size of the outbreak.
"The way to see that is [proportion of tests coming back positive]. In the UK it's now standing at 6.2% - WHO recommends a level below 5, ideally below 3%. In Germany the latest data is below 2%".
"The UK wasn't doing well in the first surge and it isn't doing very well now," Dr Roser said.
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