PATIENTS looked after in the wrong hospital department because wards are full are at greater risk of dying than those cared for in the right place, official government research has revealed.

The unprecedented study also found displaced patients - known as "boarders" - spent significantly longer in hospital and had a greater chance of being sent home only to be re-admitted.

Hospitals in Scotland are so busy that nearly one in 10 patients will be parked on a ward that does not deal with their condition at some point during their stay and a further 60% will be in hospital at a time when boarding is taking place, according to the research.

This large group, who remain in the right place despite the pressure on beds, causing other patients to be moved around, also have poorer outcomes than those who are not affected by boarding at all. Boarding puts more pressure on staff who have to look after more patients in wards.

Dr Dan Beckett, a consultant in acute medicine at Forth Valley Royal Hospital and the author of the research, said: "These patients also seem to have an increased length of stay, an increased risk of re-admission and an increased risk of mortality 30 days after discharge."

The Herald revealed more than 500 patients were boarding in Scottish hospitals on one day alone last winter. This was as part of the newspaper's NHS Time for Action campaign, which is calling for a review of NHS and social care capacity to ensure services can cope with the growing elderly population.

The Scottish Government commissioned Dr Beckett's research into the impact boarding has on patients amid concern about how often it is used to cope with the number of people requiring a hospital bed.

Anonymised details from 2.5 million hospital admissions over three years were examined for the study. Preliminary results were unveiled yesterday at an acute medicine conference ­organised by the Royal College of Physicians of Edinburgh.

These showed the average length of hospital stay among the 30% of patients totally unaffected by boarding was 2.3 days, rising to 4.2 days among those treated while boarding was occurring, and reaching 6.5 days for boarders themselves.

The proportion of boarders re-admitted to hospital within a week of their discharge was 7.5%, compared to 4.8% and 4.6% in the other two groups.

The proportion of boarders who died on the ward or within 30 days of being discharged was 4.2% - more than double those unaffected by boarding at 2% and higher than those present during periods when boarding was used, at 3.7%.

Dr Beckett warned his findings are yet to be adjusted to take into account any differences in the spectrum of age, social background and complexity of illness found in the three patient groups. Once the data has been cleaned in this way, he said, his findings were likely to be less stark but he still believes it will show boarding compromises care.

He said: "Boarders are seen less frequently by their medical teams. If they become unwell, there may be a delay in them being reviewed because medical staff are having to come from elsewhere. Even simple things such as notes being found for patients who are boarding can be more difficult because they may be kept in a different place."

A Scottish Government spokeswoman said: "Scotland is the first ­country in the UK to deal with the issue of boarding to further improve the quality of care in our hospitals.

"This work has identified that boarding can be detrimental to the recovery of patients, and that is why we are already working to reduce the boarding of patients and to ensure that, wherever possible, patients can be admitted to the right beds at the right time."