holding the reigns of power

[hatwoman]

so many times recently I've seen reins and reigns confused. but this particular mixed metaphor surely takes the biscuit. did the proof-reader not stop and think - are these reins or reigns? oh poo, they're both. something must be wrong.

to make matters worse this is the intro to a serious book about law. that area of life people by pedants supreme.

A letter to the editor/author would be in order, I feel - as you say, it's pretty obvious if you think the metaphor through.