Don't ruin this with facts counsellor.Heh. I giggled over that one, too. However, it was probably an editing error. E.g. it was probably initially written as "written whistleblowing reports" and later intended to be changed to "whistleblowing reports in writing" in order to track the language of the statute, but then someone forgot to remove the word "written".
It happens. But it's still sloppy. And it still made me giggle.
Writtwn whistleblowing reports in writing...classic