The Code of Good Practice provides that, where employers are considering dismissing an employee, they should be able to justify this drastic sanction by proving that the employee's misconduct is so serious that it makes continued employment intolerable.
One factor that could constitute such intolerability is the employee's breach of the trust relationship.
For example, the employer is entitled to claim that, where an employee is found guilty of dishonesty, the trust element of the employment relationship has been damaged.
A lie detection test only shows you that, based on the specific questions I asked him or her, measured against his or her physiological responses, the person told the truth or lied in response to the questions involved.
Therefore, if you want to dismiss an employee, you dismiss him on the basis of, not theft, but breach of trust in the relation.
Full description and details in my report to you as employer