(1) At any time after proceedings have been commenced in the Lands Tribunal but before compensation is finally assessed-
(a) the Secretary may make an offer in writing of the kind described in section 17(2)(a); or
(b) the claimant may by notice to the Secretary state an amount (inclusive or exclusive of costs) which he is willing to accept in full and final settlement of his claim or any rejected part of his claim.
(2) Where an offer made by the Secretary pursuant to section 17(2)(a) or by the Secretary or the claimant pursuant to subsection (1) is not accepted by the other party, no part of the contents of the offer which relates to any part of a claim before the Lands Tribunal shall be disclosed to the Tribunal until the amount of compensation for that part is assessed by it; but a copy of the offer enclosed in a sealed envelope may be lodged with the registrar of the Lands Tribunal and opened by it after it has made its assessment.
(3) Where the Secretary has made any offer under section 17(2)(a) or subsection (1)(a), including costs as agreed or taxed, which is not accepted by the claimant and the compensation assessed by the Lands Tribunal does not exceed the amount of compensation comprised in the offer, the Lands Tribunal shall, unless for special reason it thinks it proper not to do so, order the claimant to bear his own costs and to pay the costs of the Secretary in so far as the costs are incurred after the making of the offer.
(4) Where the claimant states an amount which he is willing to accept under subsection (1)(b) which is not paid by the Secretary and the compensation assessed by the Lands Tribunal is not less than that amount, the Lands Tribunal shall, unless for special reason it thinks it proper not to do so, order the Secretary to bear his own costs and to pay the costs of the claimant.