Let's think this through.
You are in severe housing need - currently living overcrowded in a spare room at your parent's house.
Your elderly uncle owns a house worth £400k and currently lives in that house.
Your uncle has offered to sell you this house for £230k as long as he is allowed to continue to live in the house for the next 10 years.
There are many many probems with this.
The gift - Your uncle will be gifting you the deposit of £170k, it's just the gift is in equity not cash. However this is a gift with reservation as he expects to continue to live in the property he is selling you.
The Mortgage - to get a mortgage of £230k you will need an income of at least £50k - do you have that. Also very few lenders will want to lend money to you where the person who is gifting the equity and is the vendor will become your tenant.
The 10 years your uncle has requested he stays in residence - you will become a a landlord with all of the legal and financial obligations that this entails. If you uncle proposes he continues to pay the mortgage you took out in the form of rent, if he needs help (eg claim benefits) as he is a close relative it could be deemed a "contrived tenancy" and therefore benefits will not be paid.
What happens in ten years time? Your uncle will be 82 in ten years time - what will he do then? Has he got plans to live elsewhere? If not do you have the stomach to evict an 82 year old man from his home?
I have no idea who this scheme is meant to help? You need a place to live - this will not deliver that for at least ten years, if not longer. Your uncle sounds like he needs to free up some cash - if he wants to use his home he can look in to equity release.
DO not touch this with a six foot barge pole.