Tens of thousands of cancelled operations have gone unrecorded because of a quirk in the way data is recorded, an investigation has claimed.
Figures from NHS England published in May showed nearly 75,000 NHS operations were postponed at the last minute in 2015/16 - a 10-year high.
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Hospitals must record cancellations on the day of an operation or of admission - but not those prior to that.
According to the BBC, 74 hospital trusts in England provided data suggesting they had cancelled 41,474 operations one to three days before admission within that period.
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Official NHS England figures show about 7.7 million planned operations were carried out in England last year.
The cancellations data was obtained under Freedom of Information laws.
An NHS England spokesman said: "The proportion of patients seeing their operations cancelled at the last minute remains under 1% in spite of record numbers of operations being scheduled.
"Our national data collection rightly requires trusts to focus on monitoring the number of last-minute cancellations, as this is where the most distress is caused for patients.
"Hospitals should continue to ensure that every effort is made to reschedule cancelled operations as soon as possible."
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