Senior health staff who help decide which drugs are used by GPs and hospitals are being paid to work as consultants for pharmaceutical companies who want the National Health Service to “switch” to medicines they produce.

An undercover investigation has found that some NHS staff charge up to £15,000 to organise “advisory board” meetings for drugs companies.

Many of the meetings take place in five-star hotels around the world, with some attendees telling this newspaper that they were taken to “flashy” restaurants and paid large sums while considering whether to “switch” drugs.

Health service staff who take part in “advisory boards” for pharmaceutical companies argue that their involvement helps them to make “best use” of NHS money by analysing drugs and providing expert advice.

However these disclosures will prompt concerns about a potential conflict of interest between NHS staff and drugs companies and raise questions about the impartiality of public sector staff who control budgets worth millions of pounds.

There are also concerns that, if drugs were being switched for financial, rather than medical reasons, it would not be in the best interests of patients.

NHS England and the Department of Health pledged to investigate the findings of The Daily Telegraph investigation. A spokesman for NHS England said: “These are extremely serious allegations so we have immediately directed NHS Protect to launch a full investigation of each and every case identified by this press report”.

A Department of Health spokesman said: “If these allegations are true, this is completely outrageous and amounts to an abuse of the trust that patients place in NHS staff. The NHS fraud protection body has launched an urgent investigation and we expect each Trust and Clinical Commissioning Group involved to launch a full inquiry.”