Patients undergoing major surgery in the UK are four times as likely to die as those in the US, researchers have found.
Three million operations are carried out in the UK each year
The most seriously ill NHS patients are seven times more likely to die than American patients who are as sick.
University College London and Columbia University New York researchers looked at 1,000 patients in each country.
They said a shortage of specialists and intensive care beds and longer waiting lists in the UK affected outcomes.
The NHS carries out around three million operations each year, including around 350,000 emergencies, which carry a higher risk of complications.
'Healthier and wealthier'
The researchers studied 1,000 surgery patients from the Mount Sinai Hospital in New York and 1,100 who had similar operations at the Queen Alexandra Hospital in Portsmouth.
It was found that just under 10% of the British patients died compared with 2.5% of the American patients.
The New York patients had paid for their care, so were therefore likely to have been "healthier and wealthier", the researchers said.
But they attempted to eradicate any such differences between the patient groups by giving each patient a rating based on their clinical status.
Professor Monty Mythen, head of anaesthetics at University College London, who led the study, told the Daily Mail: "In America, after surgery, everyone would go into a critical care bed in a highly monitored environment.
"That doesn't happen in the UK.
"In the Manhattan hospital the care (after surgery) is delivered largely by a consultant surgeon and an anaesthetist.
"We know from other research that more than one third of those who die after a major operation in Britain are not seen by a similar consultant."
Professor Mythen said NHS waiting lists put patients "at greater risk".
He said: "We would be suspicious that the diseases would be more advanced simply because the waiting lists are longer."
A spokeswoman for the British Medical Association said: "We have always claimed that a consultant-led service will save lives in the NHS.
"What is clear from this survey is that most of the patients in
New York were cared for by consultants after their surgery. We are critically short of doctors in the UK so this may not always be possible.
"The priority must be to increase the number of doctors in the health service."
She added: "In addition, waiting lists do not exist in the same way in the US so the patients seen may be 'healthier' than patients here in that their diseases would not have progressed to the same degree."
A spokesperson for the deparment of health said:
"It is important to note that the study focuses on comparisons between only two hospitals in the UK and USA. It would therefore be inappropriate to use this to make judgements about the national position for both countries.
"There are many differences between UK and USA healthcare systems and without a more a comprehensive analysis of the findings, it is difficult to ascertain the extent to which such factors as impact of case mix have had on the figures.
"Record investment in the NHS means that nurse, doctor and bed numbers are all rising. In fact we have recruited 6,500 more consultants, 1,600 more GPs and over 55,000 more nurses since 1997 - and together they are treating one million extra patients a year."
The research is to be published in medical journals later this year.