How will a cash back offer affect my future CGT?

Question I am in the process of buying an off-plan property, where I will get a 5% cash back upon completion. The property is being purchased for £200,000, so I will get £10,000 back upon completion. What will be deemed to be the purchase price of the property for CGT purposes.

Arthur says

Inland Revenue Statement of Practice 4/97 para 35 says that the cash back is not taxable in the hands of the recipient, but it does not deal with the purchase price of the property for CGT purposes.

I have not found anything explicit to answer this question, but from my own understanding, I would say that if the contract states that on completion there will be an automatic cash back, then the purchase price for CGT purposes is the net figure, i.e. £190,000 in this case.