NHS staff are under pressure to "magic things out of thin air" because they are being asked to deliver everything when there's not enough cash, a leading surgeon has warned.

Mr Simon Barker, the new chair of the Scottish Consultants Committee of the British Medical Association, said unless more money is put into the NHS the public will have to decide which elements of the service they can manage without.

In an interview to mark his arrival in post, Mr Barker said of the Scottish NHS: "We are on our knees now. We will be flat on our face soon. That is honestly the truth."

Already he said hospitals were having to fill consultant posts with lower grade staff because repeatedly advertised vacancies had failed to attract applicants.

This has happened following a fruitless search for a consultant psychiatrist in Aberdeen, he said, while advanced nurses are covering for paediatricians in West Lothian and consultant endoscopists in the Highlands.

"There are sometimes very sensible multidisciplinary team work-arounds, but it is not always going to be that way," he said. "The idea anyone can do any job is not realistic."

Approximately half the orthopaedic consultants appointed in Scotland in the last five years have left their jobs, according to the BMA, with only three of the 16 who quit remaining in the country.

Mr Barker, an orthopaedic surgeon in Aberdeen, said when he applied for his post 11 years ago there were eight to 10 applicants "where as now if we get one or two we think we are doing well."

Often staff were seeking a better work life balance and salary in countries such as Australia, he said.

"What we have not been good at in the NHS in Scotland is making our staff feel valued and wanted and therefore needing to stay," he said. "We are more often seen as a burden rather than an asset."

He stressed university research had found many consultants were very dedicated to their work with the Scottish health service, but also said it could be "immensely stressful" for them.

Mr Barker said: "I think on the broadest level the question is what do we as a society want to invest in healthcare - me and you as taxpayers - what do we think it is worth? At the moment we put in considerably less of our GDP than other countries of a similar size and wealth."

With a growing frail elderly population difficult questions have to be faced and discussed, he said. "The question really is for the country 'what do we want?' If we want everything free at the point of delivery to carry on, it is not possible to continue to squeeze more and more out of the same cake. You can make a car more and more efficient to a certain point, but a gallon of petrol will not drive you from Dundee to Eastbourne.

"Alternatively perhaps the country does not want to spend that kind of money on the NHS, then there has to be an honest debate about how does it want to spend the money. What things matter most.

"What we cannot do is expand and expand community care, which we need to do, whilst at the same time maintaining hospital services which are more and more elaborate and cost a lot of money... Either we need more resource or we have to be prepared to say what we can put up with not having."

He compared the situation to taking items out of a supermarket trolley because the checkout bill exceeded the cash in his wallet.

He stressed he did not see the NHS as a business, but also said "it is not as inefficient as people think".

Mr Barker added: "It is unfair to say we will fund everything and not put the money in to do it. That puts massive pressure on the managers, on clinicians and nursing colleagues and allied health professional colleagues to basically magic things out of thin air. That is not fair on the staff and that is not fair on the patients. It is like that right now."

This situation, he said, reflected a reluctance across society to face difficult issues.