awkward stairs for a banister - help please

[Griffin]

If you use a piece of base rail its unlikely that the moulding will match the handrail at the join. Using a piece of handrail and rebating it to fit around the ceiling where it meets the apron (the timber that forms the stair well opening) is the correct way to do this, as big al says, it depends on your skills versus what tools you have at your disposal.