“(1) Where a notice is given under section 42, then (subject to the provisions of this section) the tenant by whom it is given shall be liable, to the extent that they have been incurred by any relevant person in pursuance of the notice, for the reasonable costs of and incidental to any of the following matters, namely— (a) any investigation reasonably undertaken of the tenant's right to a new lease; (b) any valuation of the tenant's flat obtained for the purpose of fixing the premium or any other amount payable by virtue of Schedule 13 in connection with the grant of a new lease under section 56; (c) the grant of a new lease under that section; but this subsection shall not apply to any costs if on a sale made voluntarily a stipulation that they were to be borne by the purchaser would be void. (2) For the purposes of subsection (1) any costs incurred by a relevant person in respect of professional services rendered by any person shall only be regarded as reasonable if and to the extent that costs in respect of such services might reasonably be expected to have been incurred by him if the circumstances had been such that he was personally liable for all such costs. ........ (5) A tenant shall not be liable under this section for any costs which a party to any proceedings under this Chapter before a leasehold valuation tribunal incurs in connection with the proceedings. (6) In this section “relevant person”, in relation to a claim by a tenant under this Chapter, means the landlord for the purposes of this Chapter… or any third party to the tenant's lease.”