If the buyer is aware of the requirement at the time the buyer signs the contract, and has not had anything put in the contract to specify who should pay, then it is the buyer who will pay.
If you'd like it to the the vendor, then you need to agree it as part of the purchase price and financial agreement . If not then its over to the purchaser along with decorating and replacing windows etc.
I'd say the buyer - if the vendor does it, they'll put the price up to cover that cost. Possible to negotiate with the vendor to say how much it'll cost, and ask them to reduce the end price to allow for it - but I wouldn't hold my breath.