ask a different question and you get a different answer !
The £80k will / would be tax free ( IHT) because the estate pays the tax usually ( different in Napleonic Code countries where the lucky recipient is liable for the tax and it is commonplace for them to say ah non merci - purely on the grounds they cant afford to pay the tax that comes with the bequest )
If he is on means tested benefits, then yes that would affect them if savings are assessed ( yes this would be savings )
the benefit he is likely to be on is this
https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/372545/dwp027-102014.pdf
and yes if you read it - he would lose it - for the time he takes to spend £80k