Good cause for non-attendance at medical - Claimant or appointee?

Reg 23 Esa regs provides that “where a claimant fails without good cause to attend for…an examination, the claimant is to be treated as not having limited capability for work”.

In the case in question the claimant has an appointee. Reg 33(1) Claims and Payments regs allows an appointee, “...to exercise, on behalf of the person who is unable to act, any right to which that person may be entitled and to receive and deal on his behalf with any sums payable to him”.

Reg 33(4) states, “Anything required by these regulations to be done by or to any person who is for the time being unable to act may be done by ...the person appointed under this regulation..”

The question is which person, claimant or appointee, as a matter of law, is required to have “good cause”. My preliminary view is that it is the claimant [as 33(4) refers to things required by “these” ie C & P regs] but is anyone aware of any case law?