Thank you very much for your help! I have found an easy solution based on your advice.

In a copy of the file I used:
Find \]*\[
Replace with ^p
Use wildcards on

This removes all of the text apart from the stuff that was in the brackets and replaces it with a paragraph so that each bit from the brackets starts with a new line.
Only the first and the last bits of text don't get removed, but these are east enough to be deleted manually.

Thank you!