Elisabeth Buggins, the chair of the UK Organ Donation Taskforce, has urged people to discuss their intentions for their organs with loved ones.
She told ITV News presenter James Mates that talking about the issue helps to avoid grief stricken decisions which can burden families at times of death.
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Accompanied by the Duke of Edinburgh, the Queen will attend the opening ceremony of the fifth session in the Holyrood chamber.
Ms Leadsom has received the backing of Ian Duncan Smith, the former work and pensions secretary.
The former shadow work and pensions secretary is considered a more viable candidate than Angela Eagle, a Labour source has told ITV News.