What amounts to the “Reason for Dismissal”

What amounts to the "Reason for Dismissal"

Whose decision must be looked at when an employer engages external consultants - Kirti Jeram successfully overturns finding of unfair dismissal in the E.A.T - see judgment below

https://www.parklaneplowden.co.uk/uploads/documents/Judgment%20-%20GM%20Packaging%20v%20Haslem%20Appeal.pdf