The prime minister yesterday chaired a meeting of the government’s emergency Cobra committee but stopped short of moving the official virus strategy from the ‘contain’ phase to the ‘delay’ phase. There are four phases included in the country’s battle plan against the infection and the second ‘delay’ stage would see people being asked to work from home, schools closing and large events cancelled.

At a press conference following the Cobra meeting, England’s chief medical officer Professor Chris Whitty said the number of Covid-19 cases is expected to increase ‘initially quite slowly but really quite fast after a while’. He hinted at tighter measures aimed at protecting the public, particularly the vulnerable and elderly, which could be implemented in the next 10 to 14 days.

But former Tory Cabinet minister Rory Stewart criticised the government for not moving into the second phase already, saying Mr Johnson should be closing schools and banning big events sooner rather than later.

Speaking to LBC, Mr Stewart said that following the example of China – and his own experience leading the government against the Ebola outbreak – Mr Johnson could not afford to wait.

The London mayoral hopeful said: ‘I feel the government should be moving faster, I’m afraid there are many reasons why governments tend to be too slow, for example the costs of acting early are very very high.

‘But I would be, for example, shutting down all schools in London now.’

He added: ‘You should have no regrets about acting quickly, this is the biggest single event of this kind for 100 years since the Spanish flu, of course there are going to be significant economic costs, but better to take those economic costs immediately and keep it short and I think we are being too slow in responding.’

Mr Stewart also said he would ban large gatherings if he were mayor now and said: ‘I think the experience round the world is the more aggressive you are the better you do.

‘There are many who think the key thing at the moment is not to panic people, but I think the way you reassure people is by being honest, by being transparent about the risks, and by acting quickly and decisively.

‘If you try to reassure people by saying ‘it’s going to be alright’ that in the end undermines the credibility.’

Yesterday, the PM’s official spokesman said: ‘We remain in the contain phase but it is now accepted that this virus is going to spread in a significant way.’

Asked whether the government was being slow to act, the spokesman said the response was based on scientific advice.

‘From the beginning of the outbreak we have based all of our decisions on the best available scientific advice and we will continue to do so,’ he said.

As of 9am on Monday, 319 people tested positive for Covid-19 in the UK, up from 273 at the same point on Sunday, and five people have died in British hospitals.

The government has warned against all but essential travel to Italy and said that Britons with only ‘minor’ cold, flu or fever symptoms could soon be asked to stay at home in self-isolation.

During a Downing Street press conference, Mr Johnson told reporters the UK will almost certainly move to the delay phase of tackling coronavirus – to put off the peak of the outbreak until summer – and ‘extensive preparations’ are being made for such a move.