Life in the UK will not "return to normal" for six months, deputy chief medical officer Jenny Harries has warned.
The UK is currently in lockdown after prime minister Boris Johnson ordered people to stay at home except to shop for essentials, do one piece of exercise a day, collect medicine or go to work.
Anyone going outside must also stay at least two meters away from others in an attempt to stop the spread of the virus.
Johnson said the effectiveness of the policy would be assessed in three weeks' time to see if the measures could be relaxed.
But appearing at the daily Downing Street press conference, Harries said it would be "quite dangerous" for restrictions to be ended too early.
She said: "If we stop, then all of our efforts will be wasted and we could potentially see a second peak.
"So over time, probably over the next six months, we will have a three-week review. We will see where we are going.
"We need to keep that lid on – and then gradually we will be able to hopefully adjust some of the social distancing measures and gradually get us all back to normal.
"Three weeks for review, two or three months to see whether we have really squashed it. But about three to six months ideally, and lots of uncertainty in that, but then to see at which point we can actually get back to normal."
Meanwhile, the prime minister – who revealed on Friday that he has tested positive for the coronavirus and is now self-isolating in 11 Downing Street – has paid tribute to the 20,000 former NHS staff who have answered the call to go back to the health service during the crisis.
Johnson also revealed that 750,000 members of the public have now volunteered to help the NHS - three times the original target.
"One thing that the coronavirus crisis has already proved is that there is such a thing as society," he said.
It has also been revealed today that Johnson’s chief adviser Dominic Cummings self-isolating after experiencing coronavirus symptoms
Chief medical officer Chris Whitty is also self-isolating after reporting having symptoms.
A No.10 source said Cummings began to feel ill over the weekend, but remains “in contact” with the Downing Street operation.
Cummings was filmed by broadcasters running out of Downing Street on Friday lunchtime, shortly before the PM’s positive test was announced.
The former special advisor to Michael Gove and Vote Leave campaign director will now have to spend at least a week in quarantine, according to the Public Health England guidelines.
Johnson has continued to lead the UK response to the pandemic since testing positive, and was seen taking charge of a meeting of his senior team via video link over the weekend.
He has also posted a video from inside the flat above Number 11 Downing Street, where he is self-isolating, saying Britain's response to the crisis shows "there really is such a thing as society”.
The PM made the claim as he revealed 20,000 former NHS staff have so far answered the call to go back to work during the crisis.
Meanwhile 750,000 members of the public have volunteered to help the health service - three times the original target.
Johnson added: “It’s a most amazing thing. And that’s of course in addition to the 750,000 members of the public who have volunteered to help us get through this crisis.
"We are going to do it. We are going to do it together. One thing I think coronavirus crisis has proved is that there really is such a thing as society."
The comments are a reference to Margaret Thatcher's claim in a 1987 magazine interview that "there is no such thing as society”.
Johnson will this week write to every UK household setting out details of the government’s social distancing strategy and to urge them to stay at home, protect the NHS and save lives.
He will urge everyone to follow the rules to save lives and thank NHS staff working round the clock as well as everyone volunteering their time to protect others.
Read the letter in full here.