Four in 10 pharmacies give unsatisfactory medical advice, according to undercover research by the Consumers' Association, casting doubt on government plans for pharmacists to diagnose and treat NHS patients.

The association said yesterday that researchers from its Which? magazine visited 84 pharmacies across Britain and found the advice given in 34 was unsatisfactory.

"If researchers' symptoms during this test had been real, they could now be taking drugs inappropriate for their symptoms, or suffering with untreated serious infections or even an unplanned pregnancy," the association said.

Outlets visited included high street pharmacies run by big chains, supermarkets and small independents. The researchers posed as patients with common medical conditions.

The association said the findings were particularly worrying in light of the government's plans to expand the role of pharmacists. From later this year they will be able to prescribe medicines, issue repeat prescriptions without a doctor and sell some medicines that were previously available only on prescription.

A spokesman for the Royal Pharmaceutical Society of Great Britain, which regulates pharmacists, said the society would investigate the incidents and take appropriate action.