Thanks Wrathmonk & Background Noise.
Find and replace won't do what I want as each occurence is unique.
The long way round is for me to keep a list of drills (there are over 100 drills in this checklist) which contain a reference to another drill number and if in the future the drill numbering changes, I will have to refer to this list and then manually go through the text and change them individually.
I am sure there must be a way of dynamically linking text to avoid this
I will keep looking.
Thanks again