5. Where under regulation 41 (jurisdiction of industrial tribunals) a member or prospective member of a scheme presents to an industrial tribunal a complaint that the trustees or managers of the scheme—
(a)have committed against him an act which is unlawful by virtue of regulation 12 (pension schemes) or regulation 25 (relationships which have come to an end); or
(b)are by virtue of regulation 26 (liability of employers and principals) or regulation 27 (aiding unlawful acts) to be treated as having committed against him such an act,
the employer in relation to the scheme shall, for the purposes of the rules governing procedure, be treated as a party and be entitled to appear and be heard in accordance with those rules.