Hi, I am new to the forum so initally Hi. However i am not new to the financial / mortgage sector.
As of recent i am sure you are aware applications are significantly down, therefore any clients not 'grade A' are having problems being accepted.
Your main issue is that the 17.5% is an equitable stake in the home, many would argue this but it is a charge on the Land Registry.
This was fine in a buoyant economy with rising house prices, however in the current climate your current 80% could well be 90% in 2 years time, i.e house price falls etc.
I wish you luck, but from my experience you may well struggle..