Two in three cases of cancer are not picked up by GPs, according to research that shows for the first time how long patients really wait for a diagnosis.

Researchers said the findings were “worrying” and urged family doctors to be “more proactive” about sending patients for tests, even if symptoms were not clear cut.

The study of more than 135,000 patients with two of the most common forms of the disease found average waits of more than eight weeks for diagnosis. The vast majority of cases that turned out to be cancer were never suspected by family doctors, so were not given an urgent referral.

Experts warned that the delays were the “difference between life and death” for many patients, fuelling Britain’s poor survival rates.

The study by Cancer Research UK found that just 37 per cent of all cancer diagnoses in England involved patients who had been given an urgent referral by their GP, because the disease was suspected. Just 32 per cent of diagnoses for bowel cancer and 28 per cent of diagnoses for lung cancer were identified this way.

The study shows that without such a referral, those with bowel cancer wait an average of 61 days for a diagnosis, five weeks longer than the cases that were suspected by GPs.