NHS bosses are being paid thousands of pounds and taken on luxury trips by drugs companies lobbying for the health service to switch to their products, it has been claimed.
An investigation was launched after the Daily Telegraph reported that senior staff who help decide which drugs are used by hospitals and GPs are being paid to act as consultants by pharmaceutical companies.
The newspaper's undercover investigation reportedly discovered that some NHS officials receive up to £15,000 to organise "advisory board" meetings for drug firms seeking for the health service to switch to medicines they produce.
Many of the meetings were said to take place in five-star hotels across the world, with some attendees claiming that they had been taken to "flashy" restaurants and paid large sums while considering whether to "switch" drugs.
It raises concerns about a potential conflict of interest between NHS staff and drugs companies, and whether switches are taking place for financial rather than medical reasons.
An NHS England spokesman said: "These are extremely serious allegations, potentially involving criminal actions, so we have immediately directed NHS Protect - working in partnership with the police wherever necessary - to launch a full investigation of each and every case identified by this press report.
"These allegations also raise the question of whether this country should now legislate for a so-called Sunlight Act, requiring full disclosure of any payments made by a pharmaceutical or device company to a health professional or NHS employee."
A Department of Health spokeswoman 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 CCG (Clinical Commissioning Group) involved to launch a full inquiry and take forceful and appropriate action if any wrongdoing is found."