HTB ISA limit on shared ownership

RobertKr

I've posted this question on savings forum but I wonder if anyone used (or tried to use) HTB ISA to buy a property with price over 250k threshold (272k to be precise) but the property is new build, shared ownership. I want to buy 60% share (worth about 163k mortgage) and on the remaining 108k pay 250£ rent monthly, with 125 years lease. According to offical HTB ISA website faq
I quote
"What is the property price cap for shared ownership schemes?
In the context of shared ownership properties the price cap applies to the full sale price of the property rather than just the share you initially buy. For shared ownership properties the full sale price is a multiple of the equity share you are buying. In practice this means that if you are purchasing a 25% equity share of a property for £50,000, the full sale value is £200,000. Alternatively, your conveyancer can calculate the sale price based on the price paid for the equity share you are buying plus the net present value of rental payments due over the term of the lease.

You should speak to your solicitor or conveyancer and they will be able to advise you on whether the property you are purchasing is within the price limit and is eligible for a government bonus.
" end of quote
hence I should be able to calculate NPV value of 108k, I think its roughly (3% discount, 3k rent yearly, 125 years lease) 85k and together with 163k price of my share it total to 248k, right below limit. I struggled to find any concrete information, old guideline mention the method
but in the more recent one the section VII has been changed. I've tried to ask developer about it but no-one seems to know, they send me to coveyancer but i don'w want to start process if I cant use HTB ISA (in total in 2 about 20k saved hence potential loss of 5k bonus)