I wouldn't bother with a HIP, just go a head and market the house.
HIP's are worthless, a total waste of time!
As a buyer I wouldn't take one bit of notice of a HIP especially if I hadn't paid for this most questionable and uncomprehensive form of survey.
HIP inspectors can only make an educated guess about a property and will only have a seller's word on what has been done beneath the surface. They are mostly estate agents, or other non-engineering non-mechanical types who know next to ferk all about the fabric of a building other than what they have read in a book! Attending a 3 month course doesn't give you the knowhow and like any survey, you don't really know what a building is about until you pull it apart.
A pointless bureaucracy that serves as a hindrance and additional cost to a sale!
Your so called breach of the rules can be excused by today's announcement to scrap them.
Good job! The industry never wanted them in the first place!
Several years ago, the need was identified to simplify and accelerate the sales process of a property. The HIP was born, but failed on all counts to remedy the problem is was intended to resolve. It actually made things worse.