Pharmaceutical firms have been accused of rigging the market for thousands of prescription drugs largely not covered by national NHS price regulations.
An investigation by the Daily Telegraph found the prices of more than 20,000 so-called "specials" could have been artificially inflated.
Undercover reporters secretly recorded sales representatives for drug firms apparently offering to provide invoices for up to double their actual cost, allowing chemists to bill the NHS for sums far greater than they would spend. One firm offered to pay an annual fee to chemists who agreed to offer its prescription drugs, while a sales representative described the practice as "underhand", the Telegraph said.
Reporters posed as investors hoping to set up a chain of chemists after the newspaper was approached by a whistle-blower who alleged widespread malpractice.
Health Secretary Jeremy Hunt said the allegations were "deeply concerning". He added: "We have always been clear that NHS money should always be spent wisely for the benefit of patients. Any specific information received indicating or alleging fraud will be investigated by NHS Protect.
"Specials" are prescribed when a patient has a clinical need that cannot be met by a normal licensed medicine and can also be used to treat rare conditions.
When a pharmacist dispenses a special they are reimbursed by the NHS for the cost of the drugs, along with a £20 fixed fee, the Telegraph reported. However, the newspaper said it found that some companies were prepared to offer cash "rebates" or discounts to chemists to win business.
Jim Gee, a former chief executive of the NHS counter-fraud service and now director of counter-fraud services at BDO, the accountancy network, told the Telegraph: "Behaviour of this type diverts funds from where they are intended and undermines the provision of quality patient care. The victims are the British people and the Government need to ensure that the NHS is better protected in future."
The drugs companies said they were looking into the claims allegedly made by their representatives, while it was reported that one firm had suspended a member of staff.
A spokeswoman for Pharmarama International Limited, based in Borehamwood, Hertfordshire, said it would not comment while an internal investigation was being conducted. Quantum Pharmaceutical told the Telegraph it was investigating the allegations and had suspended a member of staff. Meanwhile, a spokeswoman for drugs firm Temag told the paper: "It would be totally unrepresentative to make any suggestion that we are involved in any sort of practice to unfairly charge the NHS."