UC, inheritance and shared ownership staircasing question

I am likely to receive a lump sum from my late mother's estate later this year. I estimate this will be something in the order of £80000. I have a shared ownership flat, with a 30% share. If I use some of this windfall to pay off my existing mortgage (£18k) would I be able to spend the rest of it on staircasing to 50% (which will be around £60k) without it being considered deliberate deprivation of funds? I am in my 50s, single, disabled and cannot work, if that makes a difference.