I believe the scales of justice are often viewed as indicating a balanced assessment of the evidence.
With respect to Lord Hutton and Dominic Grieve I suggest you think of scales in a different way, if you are to understand the truth of the matter.
Start with something that is 100% fishy.
Cover it with scales.
Those are the scales of "justice", at least when it's "justice" practised by Hutton and Grieve with respect to David Kelly.
When you hear about the scales of justice ask yourself what fishy thing those scales may be covering.