Thank you both.
I wanted to remove the comments option just for a particular course (rather than site-wide) as we are finding that some students are leaving comments to complete the assignment rather than submitting the required work as a proper submission,
AFAIK comments aren't picked up by the teacher of the course via an email notification so the teacher has to view the gradebook to pick up instances of where they have left a comment rather than a submission.
Hopefully over time students of this particular course will carry out the process correctly.