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Britons with a mild fever will be asked to begin self-isolating within the next two weeks as the coronavirus outbreak worsens, the chief medical officer has said.

Professor Chris Whitty said the UK was “very close” to imposing more stringent advice to delay the spread of Covid-19.

The first stage of this will be to ask those with a minor respiratory tract infection or fever to self-isolate within a week, and this advice would be introduced within 14 days.

“We have not reached that step but we are going to be reaching that step in the really quite near future,” Whitty told a Downing Street press conference.

“This is the first step along a path towards trying to reduce firstly the delay of the epidemic and then to pull down the peak of this epidemic so that it is smaller.”

But Whitty, prime minister Boris Johnson and chief scientific adviser Sir Patrick Vallance all stressed that the government is currently simply continuing to ask people to wash their hands for 20 seconds more regularly.

Amid questions over why the UK was not following other European countries in introducing more stringent measures, all three insisted the right action needed to be taken at the right time and that its effect needs to be backed by scientific advice.

Johnson said the UK was still trying to “contain” coronavirus but is making “extensive preparations” to introduce more restrictive measures to delay its spread in the coming weeks.

“We are preparing various actions to slow the spread of this disease in order to reduce the strain it places on the NHS,” he said.

“The more we can delay the peak of the spread to the summer, the better the NHS will be able to manage.”

Whitty said it was important not to do too much too soon because “anything we do, we have got to be able to sustain” throughout the peak of the outbreak, and there was a risk people would “understandably get fatigued” if restrictions were introduced too early.

Vallance meanwhile stressed that moves taken by countries like Italy to ban flights from affected areas, temperature test passengers at airports, and ban mass gatherings were actually relatively ineffective.

“We need to understand where we are in the epidemic and make sure that we take the actions that need to be taken at the right time,” he said.

He added the aim of the measures that would be introduced in future was to “reduce the peak numbers up to 50%” and lower the mortality rate in the at-risk group by 20-30%.

But he said it would be wrong to try to “suppress” the disease completely because it could result in a winter outbreak at a time of maximum pressure for the NHS.

“What you can’t do is suppress this thing completely, and what you shouldn’t do is suppress it completely because all that happens then is it pops up again later in the year when the NHS is at a more vulnerable stage in the winter and you end up with another problem,” he said.

Amid widespread concern about empty shelves in supermarkets due to people stockpiling products such as toilet paper, the PM also urged people to be more considerate.

He said: “We are certainly confident that we have fantastic supply chains and I know that both (environment secretary) George Eustice and (health secretary) Matt Hancock have been talking to the supermarkets to keep things moving. 

“In terms of preparations and where the public is, it is incredibly important that the public should behave responsibly and think about others.” 

Asked why he had been told not to shake hands at a Commonwealth Day service on Monday, Johnson said it was a “subliminal cue” to others to wash their hands, adding: “We were all given an instruction not to shake hands and there’s a good reason for not shaking hands, which is that the behavioural psychologists say that if you don’t shake somebody’s hand then that sends an important message to them about the importance of washing your hands.

“So there’s a subliminal cue there to everybody to wash your hands, which is, I think I’m right in saying [is] far more important.”

Handshaking was “a matter for individual choice” but was much less important than washing, he added.

Johnson will chair another COBRA meeting on Wednesday to further discuss what measures may be necessary. 

The government’s scientific advisory group for emergencies (SAGE) is also expected to meet on Tuesday. 

Attempting to address directly why the UK had not copied some of the more drastic steps of other governments, the PM concluded the press conference by saying: “The most important thing to get over is that whatever is happening in other countries, whatever measures are being urged upon us, be in no doubt we are considering absolutely all of them.

“And in due time they may, of course, become necessary.”