23. Any provision in an agreement is void in so far as it purports—

(a) to prohibit or restrict the making of protected disclosures,

(b) to exclude or limit the operation of any provision of this Act,

(c) to preclude a person from bringing any proceedings under or by virtue of this Act, or

(d) to preclude a person from bringing proceedings for breach of contract in respect of anything done in consequence of the making of a protected disclosure.