Half of adult patients receiving intravenous feeding in hospital are being poorly treated, an investigation has revealed.

More than one in four people (29 per cent) were receiving it inappropriately, and complications could have been avoided in half those treated.

Among premature babies, in almost a third of cases there were delays before the need for intravenous feeding was recognised and further delays before it was started.

A national inquiry into the provision of artificial nutrition in the NHS has found "major deficiencies" in the way it is delivered.

Good practice was found in only a fifth of the adult cases and a quarter of the premature baby cases. The report, A Mixed Bag, is the latest from the National Confidential Enquiry into Patient Outcome and Death (NCEPOD), which carries out regular, anonymous surveys of the quality and safety of medical care.

Bertie Leigh, chairman of NCEPOD, said: "It is deeply depressing that the quality of care is so often unsatisfactory. Indeed, in discussion with the NCEPOD steering committee, the scale of disappointment verged on disbelief."

Intravenous feeding is provided when a patient's gastrointestinal tract has stopped functioning because of illness or as a result of a surgical procedure. A bag of nutrient solution is infused slowly into a vein with a pump.

The most common complication is a bacterial infection associated with the catheter inserted in the vein.

The inquiry examined the care of 877 adults and 264 babies from 218 hospitals in the UK. It found that more than half the adult patients had not had their nutritional needs assessed, and some premature babies were missing out on the right nutrients to make them strong.

Mike Stroud, chair of the British Association of Parenteral and Enteral Nutrition, said: "The irrefutable data confirm what [we] have been saying – that standards in nutritional care must be improved to ensure all patients receive quality, safe and equal treatment from staff who are appropriately trained and supervised."

Health Minister Anne Milton said: "The findings of this report should be a sobering reality for clinicians and hospital boards.

"It's simply not acceptable that patients – who are already very ill – get a 'mixed bag' service from the NHS on such an important treatment."