http://www.opsi.gov.uk/acts/acts1992/Uk ... htm#mdiv38
You want to look at s38 TCGA 1992 in the link above as follows.
"(2) For the purposes of this section and for the purposes of all other provisions of this Act, the incidental costs to the person making the disposal of the acquisition of the asset or of its disposal shall consist of expenditure wholly and exclusively incurred by him for the purposes of the acquisition or, as the case may be, the disposal, being fees, commission or remuneration paid for the professional services of any surveyor or valuer, or auctioneer, or accountant, or agent or legal adviser and costs of transfer or conveyance (including stamp duty) together—
(a) in the case of the acquisition of an asset, with costs of advertising to find a seller, and
(b) in the case of a disposal, with costs of advertising to find a buyer and costs reasonably incurred in making any valuation or apportionment required for the purposes of the computation of the gain, including in particular expenses reasonably incurred in ascertaining market value where required by this Act."
And HMRC website here:
http://www.hmrc.gov.uk/manuals/CG1manual/cg15252.htm