Boris Johnson remains in hospital following his admission on Sunday with continuing coronavirus symptoms, as ministers resisted pressure to set out an "exit strategy" from the lockdown.
is currently deputising for Boris Johnson and led the Government's daily coronavirus "war cabinet".
Asked about the lockdown exit strategy for the UK, he said: "The risk right now is if we take our focus off the strategy which is beginning to work, is that we won't get through the peak as fast as we need to.
"Which is why it's perfectly legitimate to ask the question, but the Government's over-riding priority has got to be to keep up the work and the commitment that so many people have made to make sure that we maintain the social distancing, we stop the spread, we protect the NHS as we come through the peak."
Professor Neil Ferguson, from Imperial College, who has been advising the Government said he could not predict exactly when the lockdown would be lifted, reports North Wales Live.
He said: “When the lockdown ends will depend on what happens with this epidemic – how quickly case numbers decline.
“There is no point, having gone through this effort, in releasing a lockdown at a point where case numbers are still high and will resurge even faster than we have seen before.
“We want case numbers to get to a low point where we can start substituting other measures for the most intrusive and economically costly aspects of the current lockdown.
“Almost certainly those additional measures will involve massively ramped-up testing, going back to trying to identify contacts of cases and stopping chains of transmission.
“That can only feasibly be done when we have many few cases per day than we have at the moment.”
When asked about the potential final death toll, Prof Ferguson said: “It is very difficult to make predictions at the moment.
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“What we have is an exponentially growing curve of infections which we interrupted at a certain time. We can’t say in terms of the infections precisely where we are on that curve, we don’t have the ability right now to measure how many people have been infected.
“That will come with antibody tests, so we are making statistical estimates and we think it (the death toll) could be anywhere between 7,000 or so up to a little over 20,000.”
The UK's deputy chief medical officer has said some lockdown rules could stay in place for six months.
No precise exit strategy has yet been formed, though Professor Neil Ferguson, from Imperial College, who is advising the Government, said experts are looking at it in detail this week.
Ending the lockdown will rely on a substantial slowdown in the epidemic of Covid-19 – the so-called “flattening the curve” – and a downward trend, which has not yet happened in the UK.
The number of deaths is also still rising as the UK moves towards the peak of its epidemic, which is expected within the next week to 10 days.
Experts agree that much more testing is needed to get the UK out of lockdown.
At present, the UK has no real grip on how many people are currently infected and what proportion may already be immune to the disease.
The great hope is that an antibody test will soon prove reliable enough to be sold on the high street so that those people who have had the virus can resume normal life.
But these tests have produced poor results so far, and none have been deemed good enough for widespread use by Public Health England (PHE).
Once the virus is circulating at a low level, experts also hope to return to contact tracing in the hope of controlling future outbreaks.
This involves isolating individuals who have been infected, contact tracing all the people they have been in touch with and stopping the chain of transmission.