Law in relation to capital to buy a home & IR ESA

Hi Team
I know this subject has been touched upon before, but if I could ask for further clarification.
My partner is due to receive a deed of variation gift of money from his mother who was sole beneficiary for his sister who died intestate.
He is in receipt of sickness/ income related ESA which is the main income & this allows us to claim housing benefit for the local authority property in which we live. As the gift of money is looking as if it may be enough to purchase a small property - would he be able to do this & still claim his income related ESA., as he will never be able to work again due to chronic health conditions. I understand that this may be the case if the purchased property will be his main home & of course then, he can surrender the LA Property & would no longer have to claim Housing Benefit. I am trying to find the area of law within the Social Security minefield of legislation that could put his mind at rest, but I am having difficulties if finding this.
I hope you can help.
Best Wishes for 2020.

Thank you Gordon
I think I understand, but what I am trying to establish is whether or not the purchase of a home would be considered to be deprivation of capital, if this was proved for the upper tribunal case that is mentioned, I wonder what the circumstances were here & whether this could now apply to future cases.

Thank you Gordon,
that is very helpful.
Just wondering if the last came to the last & the DWP DM decided there was deprivation of capital once the purchase was made & stopped the IR ESA, would the person be able to claim universal credit instead, as otherwise there would be no money to live on. ?
Thank you .