GPs are fuelling the growing threat of antimicrobial resistance by wrongly giving antibiotics to one in five patients who has a cough or sore throat, a government-funded study has found.

Family doctors are displaying “substantial inappropriate antibiotic prescribing” when dealing with patients who have an infection, according to research published by Public Health England (PHE), the government’s public health advisers.

Of the 32.5m antibiotics GPs in England prescribe every year “at least” 20% – 6.3m – are unnecessary, a panel of experts has concluded.

They said only 10% of patients with an acute cough should be given antibiotics, but 41% received the drugs, theydiscovered when they examined GP records.

Senior doctors and Jeremy Hunt, the health and social care secretary, seized on the overprescription to urge GPs to do more to thwart the growing ineffectiveness of some antibiotics, which leads to about 25,000 deaths a year in Europe.

The findings of the study – the first to quantify the number of antibiotics issued inappropriately in primary care – has led to renewed pressure on GPs to prescribe fewer. GPs record no clinical reason for issuing the antibiotics in a third of all prescriptions, they discovered.

Most antibiotic prescriptions are issued for respiratory and urinary infections, the experts found, but GPs are giving out far too many for conditions for which they are not justified, they say in a series of five articles in the Journal of Antimicrobial Chemotherapy.

For example, ideally only 13% of people with a sore throat should get antibiotics, but 59% did when they visited a GP, the experts found. Similarly, while antibiotics are only justified in 13% of bronchitis cases, 82% of sufferers were given them.

They uncovered even bigger gaps between ideal practice and what happens in surgeries every day with sinusitis and middle ear infections. While only 11% of people with inflammation of the sinuses would benefit from antibiotics, they are prescribed to 88%. Just 17% of two- to 18-year-olds with acute otitis media (a middle ear infection) should get antibiotics but an astonishing 92% are given them.

Hunt said GPs had cut the number of antibiotics issued by 5% since 2012 but added “we need to go further and faster otherwise we risk a world where superbugs kill more people a year than cancer and routine operations become too dangerous”.

Prof Helen Stokes-Lampard, who chairs the Royal College of GPs, suggested that family doctors’ heavy workloads and the widespread shortage of family doctors were partly to blame for over-prescription.

“If GPs do prescribe antibiotics, it is because, in their expert opinion, they are the most appropriate treatment available, given the unique circumstances of the patients before us. However, we are still coming under considerable pressure from some patients who need to understand that antibiotics are not a ‘catch all’ for every illness”, Stokes-Lampard said.