How does a tribunal gauge whether an employee has been unfairly dismissed on the basis of misconduct?

In cases of misconduct a tribunal will examine first whether the employer genuinely believed that the employee was guilty of misconduct, second whether the employer had reasonable grounds for that belief, and third whether the employer had carried out as much investigation into the matter as was reasonable in the circumstances.

It is not necessary for the employer to have conclusive proof of the employee's misconduct, only a genuine and reasonable belief.