A Right of Audience is a reserved legal activity for the purposes of the Legal Services Act 2007. You cannot appear for a claimant (in the absence of the claimant) unless you have RoA as defined by para 352 of that Act. This paragraph says:
352. Meaning of 'reserved legal activity'.
'Reserved legal activity' means:
(1) the exercise of a right of audience;
(2) the conduct of litigation;
(3) reserved instrument activities;
(4) probate activities;
(5) notarial activities;
(6) the administration of oaths.
To do so is a criminal offence.