It was quite surreal talking about someone you have known all your life and you saying that they cannot look after themselves anymore.
The professionals did make it as informal as possible, but it was still quite official and 'proper'.
http://www.mental-capacity.com/abouttheact/bestinterests/index.html
http://www.nhs.uk/CarersDirect/moneyandlegal/legal/Pages/MentalCapacityAct.aspx
For a new project that I am working on (in a counselling capacity) we have been asked to use the The Warwick-Edinburgh Mental Well-being Scale (WEMWBS) as part of our evaluation and assessment.