One in seven NHS operations were cancelled or postponed on the day of surgery during one week at hospitals in the UK, a seven-day study found.
The Royal College of Anaesthetists said its findings provide the most comprehensive UK-wide study to date on rates and reasons for surgical cancellations.
They use data from 90% of NHS hospitals across England, Wales, Scotland and Northern Ireland.
It said that although last-minute cancellations of surgery were running at record highs, little was known about the specific risk factors beyond seasonal fluctuations.
Looking at the week of March 21 to 27 2017, the team noted that a total of 26,171 inpatient operations were scheduled to take place.
Of those operations, 3,724 were cancelled or postponed on the day of surgery - giving an overall cancellation rate of one in seven operations.
They found the presence of an emergency department made cancellation of surgery in that hospital five times more likely.
The data also showed that one in 10 (10%) patients undergoing elective, non-emergency inpatient surgery had previously had the same operation cancelled at least once before.
Two-thirds of these cancellations were due to non-clinical reasons, such as lack of beds (31%), insufficient operating theatre capacity (12.7%), staff unavailable (2.2%) and administration error (1.6%).
Clinical reasons accounted for a third (33%).
They found patients who were medically fit for surgery were three times more likely to have elective, non-emergency operations cancelled if they required critical care afterwards.
But those undergoing treatment for cancer were three times less likely to have their operation cancelled, those undergoing obstetric procedures were 10 times less likely to face cancellation, while those undergoing expedited surgery were four times less likely to face last-minute cancellation.
The findings come as NHS England data from the first quarter of 2018 revealed 25,475 instances of cancelled operations on the day they were scheduled - the highest since records began.
The research, published in the British Journal of Anaesthesia, was carried out in conjunction with University College London (UCL) Surgical Outcomes Research Centre.
The study authors warned that cancellations prolong surgical waiting lists, cause patients distress when they are likely to already be worried about undergoing surgery, and may result in worsened clinical outcomes.
Chief investigator Professor Ramani Moonesinghe, director of the UCL Surgical Outcomes Research Centre, said: "Last-minute cancellations of surgery affect the health and welfare of tens of thousands of patients in the UK every year.
"It is positive that clinicians appear to appropriately prioritise the most urgent cases; however, it is clear that capacity issues, in particular resulting from competition for inpatient beds with emergency admissions, and the requirement for critical care after high risk surgery, substantially influence the risk of last-minute surgical cancellation.
"There are no easy answers to these issues, but an important next step would be for hospitals to look into the reasons for cancellations locally, and for researchers to investigate the potential benefits of different solutions.
"This could include evaluating how the separation of emergency and elective services in some hospitals or specialities might reduce cancellations and improve efficiency."
An NHS England spokeswoman said: "Actually, only a tiny minority of operations - just one in 100 - is cancelled on the day, and this report provides only a selective, limited snapshot of surgery in England, where the NHS is funding more routine operations and more people are undergoing treatment than the year before."