When is a dismissal fair?

Dismissal is normally fair only if you can show that it is for one of the following reasons:

a reason related to the employee's conduct
a reason related to the employee's capability or qualifications for the job
because the employee was redundant
because a statutory duty or restriction prohibited the employment being continued
some other substantial reason of a kind which justifies the dismissal

and that you acted reasonably in treating that reason as sufficient for dismissal.