It is what it is, an old coal shed that’s been bodged about over the years to make the place more liveable, I can’t see any reason to not be able to get a mortgage on it.
how much do you want it ?
it needs a bit of facia board.
it’s probably cold as buggery in there in the winter if it was insulated badly, which it probably has been.
get a survey done and see what else is wrong.
like half the houses in England they all need knocking down and re building, nut we continue to keep patching them up.