In guidance on the practice known as parallel exporting, co-signed by the GPC and the Dispensing Doctors Association (DDA), doctors and other traders are told to stay within the law and to follow ethical guidelines.

Dispensing doctors must put patients first, followed by the wider NHS and lastly their practice.

‘Patient care must never come second to business considerations,' the DoH warns in Shortages in the supply chain of drugs, supported by the General Practitioners Committee and sent to PCTs.

‘We wish those dispensing doctors who trade medicines would stop,' said Dr David Baker, chief executive officer of the Dispensing Doctors Association, also a signatory of the joint guidance.

Any dispensing doctor selling on medicines without a wholesaler dealer's licence is committing a criminal offence, the guidance warns.

Prescription drugs are often cheaper in the UK than in the rest of Europe. This gap and the weak pound has led to dispensers, pharmacists and wholesalers selling stock on overseas.