Assisted Decision-Making (Capacity) Act 2015
12. Where an event specified in any of paragraphs (a) to (c) occurs, a decision-making assistance agreement shall, with effect from the date on which the event occurs, be null and void to the extent that the decision-making assistance agreement relates to a relevant decision where there is, in respect of the relevant decision—
(a) a decision-making order, a decision-making representation order or a co-decision-making agreement in relation to the appointer,
(b) an advance healthcare directive made by the appointer and the appointer lacks capacity, or
(c) an enduring power of attorney or enduring power under the Act of 1996 made by the appointer that has entered into force.