A qualifying employee has the right to challenge the fairness of his or her dismissal by making an application to an employment tribunal. Once such an application has been made, a dismissal is presumed to be unfair and you, as the employer, must prove otherwise. In general, statutory rights, disciplinary procedures and contractual terms must be observed and the reason for dismissal must be fair and reasonable.
The fairness of the dismissal is judged on your knowledge and understanding when you made the decision (or heard the appeal) and may not take into account anything you subsequently learnt.
Redundancy is also a potentially fair ground for dismissal but may also be considered to be unfair if appropriate redundancy procedures and decision-making issues are not observed.