The primary power for appointeeship is in the Social Security Administration Act 1992, detailed in section 5.
This gives the power to make the appointee regulations. For older, legacy benefits, it is Regulation 33 of the Social Security Claims and Payments Regulations 1987. For the new style benefits, that is, Employment Support Allowance, Job Seekers Allowance, Personal Independence Payments, and Universal Credits, it is regulation 57 of the Claims and Payments Regulations 2013
Appointeeship is not actually governed by the Mental Capacity Act 2005. That was deliberate because the DWP wanted to retain control of the appointeeship process and detail. However, the Act’s five underpinning principles are built into the appointeeship process.
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