The NHS is to crack down on sponsorship deals in which commercial firms pay for health service staff and equipment in exchange for "endorsement" of their products, amid fears that such arrangements are compromising clinical judgments.

The move could lead to the tearing up of thousands of contracts worth millions of pounds every year to the NHS, and which help pay for specialist services which otherwise might not be provided by the health service.

Such sponsorship deals are often connected to the care of chronic conditions such as continence nursing, epilepsy, Parkinson's disease, and multiple sclerosis, but are also used as a marketing tool by suppliers of products such as prosthetic hips.

The crackdown will dismay some patient groups because it will potentially threaten the provision of services.

New guidance forces NHS trusts to review all agreements in which suppliers meet all or part of the cost of certain staff members, provide discounts on drugs and equipment, or subsidise research and training, in return for contracts.

Ministers do not want to prevent "collaborative partnerships" with private sector suppliers, but want to ensure that such deals "should always be based upon clinical evidence that the product is best for their patients".

The guidance expressly outlaws deals whereby sponsorship is linked to the purchase of particular products, or use of a particular supplier - although there is evidence that many trusts are tied in to such contracts.

More than 360 of the UK's 600 nursing posts dedicated to stoma care - treatment following bowel surgery such as colostomy - are financed by the suppliers of stoma bags in deals worth up to £100,000 per year to a trust.

According to the Royal College of Nursing, some stoma deals stipulate that a certain proportion - as much as 50% - of patients treated at a particular trust should be fitted with the sponsoring companies' stoma bag.

Some deals stipulate that the sponsor should be the sole dispenser of stoma care equipment to the patients at home - a non-skilled distribution job that is worth up to 25% of each item bought by the NHS.

Julia Breeze, who chairs the Royal College of Nursing gastroenterology and stoma care nursing forum, said it would be difficult for many trusts to pull out of sponsorship deals without threatening services.

"We are an expensive commodity and the money isn't there for us otherwise - there are so many competing needs in the NHS these days," she said.

Ray Hodgkinson, director of the British Healthcare Trades Association, admitted that sponsorship was used by firms as a way of increasing sales. But he added that many such deals were initiated by the NHS itself.

A recent house of commons public accounts committee report revealed that five NHS trusts had admitted to auditors that their choice of artificial hip supplier was influenced by the "incentives" on offer, including free equipment and research funding.

The Royal College of Nursing is to produce its own guidelines on sponsorship in the next few weeks in a bid to stamp out unnaceptable sponsorship deals. It said stoma company "inducements" to nurses have included company cars, mobile phones and free air miles.