The staircase here goes up to the tower from the first floor, but after the first landing there's a low beam obstructing passage. It appears not to have been added later, but perhaps the whole thing needed reinforcing and there's a steel beam in there. Unfortunately, the National Trust didn't have any information displayed about why it was like this.

<a href="https://commons.wikimedia.org/wiki/File:Staircase_at_Woodbridge_House.jpg" rel="noreferrer nofollow">commons.wikimedia.org/wiki/File:Staircase_at_Woodbridge_H...</a>