Most investors, whether personal landlords or companies, will have suffered some abortive costs for deals that failed.
The nature of the costs will be capital for investors.
BIM35325 – Capital/revenue divide: general themes: abortive expenditure
Expenditure that would have been capital had it been successful does not change its character merely because in the event it is abortive. ECC Quarries Ltd v Watkis  51TC153 was concerned with costs incurred in an unsuccessful planning application.
If the application had succeeded the expenditure would have been capital. In the event the application failed; no asset was acquired or modified (and the company did not rid itself of any disadvantageous asset).
What this means is that property investors don’t get any tax relief for abortive fees.
This can be extremely bad news as the case of Hardy v Revenue & Customs  UKFTT 250 (TC) a 10% deposit was paid and the outcome was that HMRC disallowed the claim for relief, the taxpayer appealed and the appeal was dismissed.
It seems unfair but the seller who receives the deposit treats it as a capital gain and pays tax on it.
If a property trader/developer had suffered the loss of the deposit and the costs was ‘wholly and exclusively’ for the purpose of the trade, the expenditure might be an allowable deduction from profits.