(1) If a health and safety representative, or deputy health and safety representative (if any), represents a designated work group of the employees of more than one employer—
(a) the costs of the representative exercising powers under this Part; and
(b) the costs mentioned in section 67(4)(b)—
for which any of the employers are liable must be apportioned equally between each of the employers unless they agree otherwise.
(2) An agreement to apportion the costs in another way may be varied at any time by negotiation between each employer.