An "opt-out" system of organ donation may see patients' wishes blocked by relatives, experts will warn next week.

The British Medical Association has urged the use of a "soft opt-out" system to increase the number of life-saving transplants that take place.

However, the event at Stirling University on Monday will hear that doctors will almost always defer to the wishes of bereaved relatives even if they conflict with the wishes of the deceased.

In many countries, next of kin can block organ donation even if the person who has died has not opted out themselves. Speakers at the event include Professor Magi Sque of Wolverhampton University and Dr Ben Saunders, of Stirling University.

Dr Saunders said: "Different countries have different systems. If the individual does not opt out and is treated as a donor the next of kin can still opt out. But maybe that person actually wanted their organs to be used – it can mean over-riding an individual's wishes."