Patients who miss GP appointments are costing NHS England £216m a year, officials have said.
Data shows more than 15 million consultations are being wasted because patients fail to show up.
NHS England said cancelling appointments would free doctors, nurses and other professionals to see people who need care and attention.
The British Medical Association urged patients to "play their part" to help the NHS cope with rising demand.
NHS Digital GP appointments data shows more than 1.2 million GP hours are being wasted each year.
NHS England said each appointment cost an average of £30 and the overall expense of patients not cancelling appointments could pay for the annual salary of 2,325 full-time GPs.
'Every appointment precious'
Dr Nikki Kanani, acting director of primary care for NHS England, and a GP in south-east London, pointed out that £216m could also fund about 58,000 hip operations or 220,000 cataract operations.
She told the BBC: "When a patient misses an appointment, my first instinct is to worry. I worry why that person has missed that appointment but then I can't use that time for somebody else.
"So I'll check up on the patient but I'm not able to get anyone else in."
Dr Kanai said it was becoming increasingly easy to manage appointments through the online access offered by many surgeries. adding: "Our message is clear. If you cannot make it to your appointment or no longer need a consultation, please let your GP practice know in advance."
Prof Helen Stokes-Lampard, chairwoman of the Royal College of GPs, said: "There may be many reasons why a patient might miss an appointment, and in some cases it can be an indication that something serious is going on for that individual – but we would urge patients to let us know if they can't attend as soon as possible."
Dr Richard Vautrey, the BMA's GP committee chairman, said: "Every appointment at a GP practice is precious, especially at a time when GP services are struggling to cope with rising patient demand, staff shortages and inadequate budgets.
"Practices will try many ways to address this problem, but ultimately patients do need to play their part."
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