An overwhelming majority of doctors fear the NHS is not well prepared to deal with a major outbreak of coronavirus, a survey has found.

More than 99% of 1,618 NHS medics questioned appear not to agree with the assurances given by Boris Johnson that the service will cope if it is hit by a surge in the number of people falling ill.

Doctors are worried that the NHS is already stretched and under heavy pressure, and especially that it has too few intensive care beds and that GP surgeries are struggling to meet patient demand.

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“Yesterday Mr Johnson said he was ‘very, very confident’ the NHS would be able to deal with an outbreak of Covid-19. Our survey shows that frontline doctors don’t agree,” said Dr Rinesh Parmar, the chair of the Doctors’ Association UK, which undertook the survey.

“The truth is the NHS has already been brought to its knees and many doctors fear that our health system simply won’t cope in the event of influx of coronavirus patients.

“With nearly 10,000 doctor vacancies and 43,000 nurse vacancies [in the NHS in England] the NHS is already understaffed to deal with demand. A&E waiting times are the worst on record. Intensive care units are at capacity and are even struggling to admit patients who are critically unwell or awaiting cancer surgery.”

Survey respondents were asked: do you feel the NHS is well prepared for coronavirus? Only eight of the 1,618 who replied said they thought it was. The survey was a self-selecting rather than representative sample of the UK’s medical workforce.

The prime minister said on Sunday the NHS had plans in place and the resources to deal with large numbers of people falling ill because of the virus. Thirty-six cases have been confirmed across the four home nations so far, 32 of them in England.

Speaking at a Public Health England laboratory in London where swab samples from people who may have the virus are tested, Johnson said: “I think the crucial thing for the public to understand is coronavirus is of concern, it is a novel illness, but it’s something this country really amply has the resources to deal with.

“We have state-of-the-art testing facilities, we have a fantastic NHS. We will have to get through this, but believe me we are going to beat it.”

The main concerns doctors highlighted in the survey were:

The NHS is already struggling to meet the existing need for care and so would not be able to cope with a sudden large increase in demand linked to Covid-19.

Hospitals have too few intensive care and high-dependency care beds, those units are understaffed and there are no plans to expand such facilities.

GP practices do not have enough appointments to ensure that patients can be seen quickly.

Some hospitals are lacking basic equipment including face masks.

NHS 111 is still telling some people who appear to have symptoms of Covid-19 to go to A&E or an urgent care centre, even though official advice warns against anyone with suspected coronavirus going to A&E or a GP practice.

Parmar said doctors had been “shouting this from the rooftops for some time”. Many hoped the threat of Covid-19 would prompt an honest conversation to address the issue of critical care capacity and our ability to look after our sickest patients. By repeating ‘the NHS is well prepared to deal with coronavirus’, it seems that yet again doctors’ concerns have been brushed under the carpet.”

Some hospital trust chief executives privately harbour similar concerns.

An NHS spokesperson said the service was well placed to respond to a surge in cases. They said: “The NHS has well-established escalation plans in place, and hardworking staff are working round the clock caring for those who have contracted the coronavirus and putting measures in place to help stop it spreading.”

The Guardian approached the Department of Health and Social Care for a response to the survey findings.