Bereaved relatives are the main reason behind Britain's shortage of organs for transplantation, researchers said today.

A two-year study of UK hospitals found 41% of bereaved relatives refused to give consent for their loved one's organs to be donated.

The researchers - led by Chris Rudge from the NHS organ matching body, UK Transplant - said Britain has one of the lowest deceased donor rates in western Europe at just over 12 per million of the population.

Their study, published in the British Medical Journal, said that the number of brain-dead organ donors had been between 644 and 739 a year since 1998.

Other European countries have donor rates of between 13 and 22 per million, with Spain having the highest rate at 33 per million.

The researchers conducted a two-year audit of all deaths in 341 intensive care units at 284 UK hospitals to try and identify potential donors.

Over this period, the families of 94% of patients who could have been donors were asked for permission to use their loved ones' organs, with 41% refusing to give consent.

The main reasons for opposing transplantation included relatives not wanting the body to be damaged by surgery, not being sure whether the patient would have agreed to donation, and disagreeing about the decision.

In the case of families from ethnic minorities, the refusal rate was 70%, twice that for relatives of white potential donors. The age and sex of the potential donor had no influence on whether or not consent was given.

"Intensive care units are extremely good in considering possible organ donation from suitable patients," the researchers wrote. "The biggest obstacle to improving the organ donation rate is the high proportion of relatives who deny consent."

The maximum potential donor rate during the study period was 23.2 per million per year - still much lower than the actual rate achieved in Spain.

Researchers said the Human Tissue Act, which comes into force in September, could help to address the problem. Under the legislation, the wishes and consent of individual donors will be paramount.