I need to change the direction of my stairs in order to reach a bathroom that at the moment can only be accessed through the main bedroom.
Do you think that it would be a major job to maintain the supporting walls of the staircase (middle partion of terraced house/ ground floor) take out the original stairs and put in a new lot that go in the opposite direction?
Reversing the stairs can be done, and is MUCH less work than moving them through 90 degrees. Often this is done and then a wall put up in the bedroom to make a corridor for accessing the bathroom.
I would contact someone who specialises in staircases, rather than a general builder. All the making good afterwards etc may or may not be a diy job depending on your skill level and whether you have the time.
Bear in mind that you will need a way into the stairs at the bottom, as you'll now be accessing them from the other end. Also, at the top end of the stairs, you will need access out to the new corridor. Are these wall solid brick, or stud wall, or is there a door there already for a cupboard?
That's a big bonus as it means you shouldn't need to have any brickwork altered or doors put in apart from the one between the new corridor and the bedroom. Possibly the door which is currently on the over-stairs cupboard could be reused for this, and the old doorway either opened up to ceiling height or made into an arch for entry from the new staircase to the corridor.
Another thought is that the lightswitches and maybe sockets would have to be moved, and plus you would need a light in the corridor.