The Administrative Review Council identifies the main difference between a merits review and a review by a court as:
'A court will review a decision only on the ground of legal error. It will not set a decision aside simply because it prefers a different decision or factual finding. The Ombudsman, internal review officers, and some appeals tribunals and investigatory bodies can examine errors in fact findings as well as legal errors. For example, they can consider whether a decision is based on incorrect information or attaches too much or too little weight to particular evidence.'
From Decision Making: evidence, facts and findings, Administrative Review Council Best Practice Guide 3, August 2007, p 1.