GPs overprescribing antibiotics is significantly damaging the survival chances of cancer patients, leading oncologists have warned.

A major new NHS study has found that sufferers undergoing the latest cancer treatments survived for only half as long if they were also taking the common infection-fighting drugs.

Family doctors have been warned to “think really carefully”, before prescribing antibiotics after the analysis of more than 300 patients at the Christie Hospital in Manchester concluded the drugs were wiping out gut bacteria crucial for fighting cancer.

The warning comes amid escalating concern that the profligate use of antibiotics by doctors has fuelled the rise of lethal drug-resistant superbugs.

Researchers analysed data from 303 patients with melanoma, renal and non-small cell lung cancer being treated with immunotherapy drugs, known as checkpoint inhibitors, between 2015 and 2017.

Survival rates among patients who took antibiotics - at any stage from two weeks before their cancer treatment started, to six weeks after treatment - were compared with those of patients who took none.

The antibiotic group survived for an average of 317 days, while those who had not taken antibiotics survived for 651. Meanwhile those who had used antibiotics over a longer period or been given multiple types of the drug had an even lower survival span of just 193 days.