If, after all practicable steps to support a person to make a decision have been taken, there is a concern that a person lacks the capacity to make a specific decision, their capacity must be assessed. The test is as follows:
A person is deemed to ‘lack capacity’ in relation to the decision in question if he or she is unable to make a decision for himself in relation to the matter because of an impairment of, or a disturbance in the functioning of, the mind or brain.
It must be possible to explain how the impairment or disturbance has caused the inability to make a decision. In other words, there must be a causal link.