They said services would be severely tested as temperatures plummet and there is a significant rise in flu, norovirus and respiratory conditions.

In a chilling caution of the potential trouble ahead NHS Providers, which represents health service acute, ambulance, community and mental health services, said it was “not where it would want to be” heading into winter.

The crisis was laid bare in a briefing paper on how trusts were preparing for the months ahead which said there were still “risks” in the system.

These include a more virulent flu strain, problems with capacity, workforce shortages and pressurised finances.

Bed occupancy rates were running above the recommended safe levels with 87.1 per cent already full. It means there was “very little give in the system”.

The Society for Acute Medicine, which represents hospital doctors who look after patients admitted emergencies who do not need surgery, said the NHS was 1,400 beds short of what was required.

President Dr Nick Scriven said: “The fear is that we have not faced an infection crisis over winter for several years and if the Australasian experience is repeated here the system will be swamped as never before.

“There is a real sense of foreboding that this may be the winter that finally breaks the backbone of the service.”

More than 34,000 people died as a result of respiratory diseases in England and Wales during the 2016/17 flu season.

It was the second highest toll in five years and a “significant increase” on the previous winter total of just over 24,000.

The figures were released by the Office for National Statistics, which said the rise was “likely due to the predominant strain of flu prevalent during the 2016 to 2017 winter which had greater impact on the elderly than the young”. Charity chiefs said a third of older people do not get the flu jab.

Caroline Abrahams, of Age UK, said: “We would encourage any older person to make sure they receive the jab every year as it offers valuable protection against the virus and anything that can be done to help prevent older people from contracting flu is worth doing. We cannot run the risk of these figures getting even worse next year so the Government must take urgent action to address the underlying causes.”

The briefing paper warned this year’s flu strain was “potentially the worst we have seen in two decades”.

Health chiefs are bracing themselves for an outbreak similar to that seen during the flu season in the Southern Hemisphere where hospitals were forced to close their doors to new patients and people faced long waits. Other problems include shortages of key staff groups including paramedics, GPs and A & E consultants and nurses.

Chris Hopson, chief executive of NHS Providers, said: “Winter always presents a big challenge to the NHS.

“Last year the pressures were intolerable. Services were stretched up to, and in some places beyond breaking point.

“This time preparations have never been more thorough. But we have to recognise we are not where we would want to be as we head into winter.

“The NHS is already under severe pressure, and while the additional funding in the recent Budget is welcome, it has come very late to be used to maximum effect.

“We can not say with certainty how tough this winter will be, but the likelihood is that services will be sorely tested. We must hope the considerable efforts to curb the impact of flu are successful.”