Hi dale,
HMRC cannot give clearance before a gain is declared.
We can only signpost you to the guidance at CG15120 which is limited to the four categories for expenditure allowable under TCGA92/S38 and no other expenditure is allowable unless specifically provided for by TCGA92/S38.
CG15250 covers incidental costs of acquisition and disposal which are allowable and regarding your question, only fees, commission or remuneration paid for the professional services of any surveyor, valuer, auctioneer, accountant, agent or legal adviser are allowable.
It is important to remember that the taxation of capital gains is concerned with the gain on the disposal of assets and not the finance costs connected to the transaction.
The expenses you describe does not appear to meet any of the examples listed at CG15250 but under Self Assessment principles it is your responsibility to make the final decision based on the available guidance.
CG15120 - Deferred consideration: unascertainable: election for treatment of loss - necessary adjustments
Thank you.