I have personal experience of house alterations, but I live in Scotland which is very different to England.
Before I developed PD I had suffered from a motor neuropathy which severely restricted walking distance and because of reduction in thigh power, stairs were a real problem. When I was discharged from hospital after a string of tests and investigations, the local OT called round and decided that I needed a stairlift and a converted bathroom to create a wet room with grab rails and folding shower seat - for when I got worse.
She then contacted Argyll Care and Repair. This is a council funded organisation who arrange contractors and grants. Anyone can apply for a grant covering 80% of the cost. This is not means tested. On low income, 100% grants are available.
Thus, a £5000 stairlift cost £1250, a £6000 bathroom £1500.
The council pays this because it is cheaper to keep folk in their own homes than in care homes. Any further adaptations will be funded similarly.
Furthermore, if you convert a room to make a special bathroom, you get a reduction in council tax by one grade.
So although PD has considerably worsened my mobility, everything is already in place to allow me to carry on at home.
This, I'm afraid, is the difference between a government that is committed to the welfare of disabled folk, and one that isn't.
(I should add, a straight stairlift is about half the price I paid, our stairs have a half landing and double back.)