Patients who have emergency surgery on the weekend are 11 per cent more likely to die in the 30 days after the operation, compared to people treated on weekdays, new research has found.

The research examined staffing levels in 156 NHS hospitals and found patients who go to less well staffed hospitals are 7 per cent more likely to die than in better-staffed hospitals.

Experts at St George's, University of London, found that three main factors were associated with whether a person is likely to survive 30 days after emergency surgery: the day of the week the patient was admitted and the number of consultant doctors, and nurses working.

Patients were also seven per cent more likely to die if a smaller number of junior doctors were rostered in general surgery, the study found.

Peter Holt, the lead author of the report and a vascular surgeon from St George's, University of London, said hospitals with higher staffing ratios had the best outcomes in terms of patients' survival rates.

"This is the first analysis on this scale for emergency general surgical admissions examining associations between the numbers of senior doctors, junior doctors and nurses and survival rates," he said.

"Although we have not demonstrated causation, we believe the findings should form an important part of the debate over disparities in staffing levels and resource provision between NHS Trusts."

The best performing hospitals in the study had 60 per cent fewer deaths. This was attributed to 40 per cent more surgeons per bed, 38 per cent more junior doctors per patient admitted and 24 per cent more nurses per bed, despite the better performing hospitals treating a higher number of patients with significant pre-existing medical problems.

Almost 300,000 emergency admissions were analysed, Mr Holt said, but the findings centred on the outcomes after emergency surgery, including abdominal surgery, appendix removals, hernia repair and acute pancreatitis, rather than elective procedures.

"The results of this research suggest that retaining the medical and nursing workforce is critical to delivering the best outcomes for emergency surgical admissions. It has been observed that there is an elevated death rate for patients admitted at weekends - this may be because on average patients are more unwell than during the week," he said.

"However, in order to address inequalities in outcome that may exist across the week a significant increase in funding would be needed in the NHS, for the recruitment of staff and improvement in facilities. The required increase in funding could be as high as 40 per cent."

The research has been published in the British Journal of Anaesthesia.