When it comes to nested parentheses, there are two options. (The first is to use square brackets for the inner text [like this]. The second is to use parentheses again (like this).)
I believe that nested parentheses should be avoided where possible. But in case they are inevitable, I can see a drawback to both approaches. Square brackets can be confusing since they are more commonly used for other purposes, while nested parentheses can give the reader a hard time keeping track of which parentheses were closed.
APA suggests using square brackets for the inner text. The Chicago Manual of Style also suggests this, but it also mentions that
British style is to use parentheses within parentheses.
I also found this guide, which suggests that UK English uses parentheses throughout.
So, my question is, which British manual of style suggests using nested parentheses? I found some British manuals of style that I could check, like “New Hart’s Rules: The Handbook of Style for Writers and Editors”, but they are not freely accessible online.