Coronavirus is "holding a gun" to Boris Johnson's head and it will not be long before the NHS is stretched in the north of England, an expert has warned.
Professor John Edmunds, a member of the Government's Scientific Advisory Group for Emergencies (Sage), said his criticism comes when he feels politicians do not recognise the peril they are in.
Speaking online as part of the Royal Society of Medicine's Covid-19 Series, Prof Edmunds said policy makers had to make dreadful decisions about restrictions.
He said: "I don't think it's us (scientists) holding the guns to the Prime Minister's head, I think it's the virus."
Prof Edmunds added: "It's not our decision. It is their decision, it is a dreadful decision.
"There is no way out of this where harm isn't done, and you're balancing harm to one sector of society, in order to protect other sectors of society, and so on.
"It's dreadful. I have huge sympathy for the politicians that have to weigh up these things and come to a decision.
"And yes, sometimes I sort of criticise them for it, if I feel that they're not realising that the gun is pointing straight at their heads."
Prof Edmunds, who is advising the Government's coronavirus response, added that there are options that can be comparatively good for the economy and for the epidemiology, and that early intervention which can be applied quickly and then harshly eased could be good.
He explained: "That is much better for the epidemiology and I think may well be better for the economy as well."
Prof Edmunds also warned that the measures were necessary to stop the epidemic getting out of of control and to ensure the NHS is not overwhelmed.
He said: "But, in the north of England now, we are not that far away from the health service being stretched.
"Because even if we turn the epidemic around now, infections that occur today won't go to hospital for another week or two."
The professor of infectious disease modelling at the London School of Hygiene and Tropical Medicine also said many people will die if the infection runs its course, and people need to act together to keep it at bay.