More than a month into the latest national lockdown, some scientists and politicians are at odds over when the UK will be able to lift the restrictions.
Boris Johnson has said he hopes a "gradual and phased" relaxation of coronavirus measures can begin early next month, with the reopening of schools in England from 8 March.
But senior Tory MP Mark Harper has called for all restrictions to end once vulnerable groups - including all over-50s - have received their first vaccine dose.
With the UK announcing nearly 20,000 new coronavirus cases on Friday, former health secretary Jeremy Hunt has suggested lockdown restrictions should remain until daily infections fall to below 1,000.
Now one of the government's scientific advisers has told Sky News it could be "months" before most of the measures are gone.
So when is the UK likely to be able to end the lockdown? And what factors should decide that restrictions can be lifted?
Will vaccines be enough to lift lockdown?
The government has revealed it wants all over-50s to be offered a vaccine by May, while a recent study suggests the Oxford-AstraZeneca jab might also reduce the spread of the virus.
But is vaccinating the vulnerable enough to lift lockdown restrictions?
Professor Kamlesh Khunti, a member of the government's Scientific Advisory Group for Emergencies (SAGE), said any suggestion that all restrictions can end in May is giving people "false hope".
"Not everyone will have had the two shots that's required by May - that's not going to happen," he told Sky News.
"For the AstraZeneca vaccine we've seen that there may be a signal that transmission is reduced. We don't know that about the Pfizer vaccine yet.
"We also don't know the effect these vaccines will have on mutations.
"All of this needs continuous monitoring. You can't just say we'll open everything up in May. You're giving false hope to the public.
"Everyone is frustrated, everyone is fed up with this. We don't want to go into another lockdown. That's why it needs to be careful and done in a planned way."
What measures need to be considered to lift lockdown?
Prof Khunti said the number of daily COVID-19 cases as well as the UK's coronavirus reproduction rate - known as the R value - and the effect of schools reopening on infection numbers should determine when lockdown can be lifted.
Potential new variants of the virus would also have to be considered, he added.
"We're talking months here," Prof Khunti told Sky News.
"Once schools are open, you can't just open everything else up. You need to monitor and see what effect opening schools up is having.
"If you open everything at the same time, first of all there's a danger we may go back into lockdown again quickly.
"Secondly, you want know what is increasing the number of infections.
"If you do it gradually, you can monitor it and feel it is safe to open the next thing - whatever the next thing is. I presume that will be the retail industry.
"It's really, really crucial the rates are down."
Should lockdown be lifted when daily cases fall below 1,000?
But Prof Khunti said was "very surprised" to see Mr Hunt's remarks that the UK should keep restrictions until cases fall below 1,000.
"It's really difficult to pluck a figure out of 1,000. I'm not sure where we get that figure of a 1,000 from," he said.
"Is it 1,000 cases? Is it 10,000 cases? Certainly it needs to be well under 10,000 cases but no one can tell you the exact figure.
"If you look at some other countries, such as Australia and China, in a city when they had 300 cases, they shut the whole city down."
What about the positivity rate?
Another crucial metric to understand the evolution of the pandemic is the positivity rate, which is the percentage of people who have tested positive for COVID-19 out of the number of tests carried out.
The World Health Organisation said in May the positivity rate should be under 5% to have the pandemic under control.
Prof Khunti said a low positivity rate was important but if the number of cases remain high it is "still a problem".
He added that the impact on the NHS was also an important factor in the decision when to lift lockdown.
"There are still some intensive care units that don't have any spaces," he said.
"Overall we are seeing stability and some decline. It's a massive challenge for the healthcare system, having hospitals completely full with patients because all the other activity can't happen.
"If we can get the community cases down, that will translate into less numbers of people being hospitalised."
Prof Khunti also warned the government against imposing different restrictions in different parts of the country when lockdown is eased.
"It causes a lot of confusion in the community," he said.
"Ideally you want the same measures for the whole country. You may now and again get a surge in one area where you need to get in there quickly, just like we've seen with the seven postcodes where they're doing door-to-door checking."