Supplies of vital medicines, including those used in the fight against cancer, are running short because UK pharmacies and drug wholesalers are selling them abroad to maximise profits.

The situation is becoming so critical that last night major pharmaceutical companies and leading charities called for the government to introduce new regulations to ensure supplies will be guaranteed in the future.

The shortage has been caused by the falling value of sterling which has meant that UK pharmacies and drug wholesalers can earn greater returns by selling medicines to the continent. An agreement between the pharmaceutical companies and the government earlier this year to cut the price of drugs sold to the NHS by 3.9 per cent has also made medicines intended for distribution in the UK more attractive to foreign buyers. As a result, exports of expensive branded prescription drugs from the UK are soaring, resulting in shortages in the supply chain. Last night leading cancer charities expressed alarm at the situation. "Cancer Research UK urges the Department of Health to ensure that no patient experiences any delay in getting prescription drugs," said Hilary Jackson, the organisation's policy manager. "We are concerned to hear of cases where patients have been delayed access to prescribed medication or have to find an alternative supplier. This causes extra distress at an already difficult time."

As a growing number of patients report problems sourcing their prescription drugs, the pharmaceutical industry has confirmed it is holding urgent talks with the government to guarantee supplies of vital medicines.

The trade in drugs across the EU is permitted under the laws of the common market, although there are rules governing how much each pharmacy can sell. But as the UK supply chain connects some 12,500 pharmacies, 400 hospitals and 4,000 dispensing doctors' surgeries - in addition to some 1,800 wholesalers who hold export licences - regulating and monitoring the sale of drugs abroad is problematic. The result is that patients may face a postcode lottery when it comes to sourcing their drugs.

"There are pockets of shortages in the UK," confirmed David Fisher, commercial director at the Association of the British Pharmaceutical Industry. "The situation has been created largely because medicines in the UK are cheap compared with other parts of Europe."

A spokeswoman for the Swiss pharmaceutical giant Novartis said it was aware there were problems with a shortage of Femera, used specifically for post-menopausal women with breast cancer, in some parts of the country. "Novartis is committed to ensuring a reliable supply of its medicines for the UK," she said. "To ensure that patients will always be able to receive essential medicines, such as Femara, we have in place an emergency supply procedure. Pharmacists can contact Novartis customer care who will work to supply medicines in situations such as this."

A Department of Health spokeswoman said: "The department is aware of concerns about the supply of medicines. We are monitoring the situation closely and are in regular contact with pharmacists, pharmaceutical companies and wholesalers." Last month the Pharmaceutical Services Negotiating Committee, which represents pharmacies in England and Wales, called for regulatory action to guarantee supplies. The committee claims pharmacies are now spending around an hour every day sourcing medicines for their patients.