A patients' group today called for an investigation into the medicine supply chain after two batches of fake drugs were found for the first time in 10 years.

Yesterday, the government's medicines watchdog said counterfeit anti-obesity tablets had been discovered, only a week after fake tablets of Cialis, an anti-impotence drug, were found.

The Patients' Association said there were serious questions about the integrity of the medicine supply chains in Britain and across the European Union.

The association's director of policy, Simon Williams, said: "Clearly, scaremongering will not help anyone.

"Nonetheless, the Patients' Association believes that the discovery of counterfeit medicines should prompt a radical reassessment of the integrity of the EU and UK medicines supply chain.

"We are increasingly concerned not just about counterfeit medicines, but also the growth of unregulated internet pharmacies and the patient safety implications of repackaging medicines."

Mr Williams said he was relieved the fake Cialis was inactive and would not have harmed any of the patients who took it. But if the fake tablets had claimed to lower blood pressure or treat epilepsy, the consequences would have been serious.

"There is a fundamental difference between buying a product from an unregulated online source and receiving a medicine in the legitimate, tightly-regulated supply chain," he said. "Finding a counterfeit in the latter should be a cause for serious scrutiny and concern."

The last time fake drugs were uncovered was in 1994 when a counterfeit batch of tablets to treat peptic ulcers and stomach acid was found.

Yesterday it emerged that a wholesaler had noticed suspicious batch numbers on a box of tablets claiming to be anti-obesity drug Reductil.

The Medicines and Healthcare products Regulatory Agency (MHRA) launched an investigation to see whether there was a link between the Cialis and Reductil cases.

Kent Woods, chief executive of the MHRA, said: "Although the safety of counterfeit medicines cannot be guaranteed, there is no indication from testing of the counterfeit product that it poses an immediate risk to patients. If patients have any concerns about possible side effects they should consult a doctor."