Have they given you a job description or person specification? If so, you could prepare some examples of times where you've dealt with situations that show where you meet the specification for the role.

If I were interviewing I might ask something along the lines of:
Tell me about the most challenging employee relations case you've dealt with.
What role did you play in the situation?
What was the outcome?
Was it the right outcome?
What did you learn from it?

I'd be looking for a clear, fairly short precis of the case, an awareness that the HR role was to advise and coach the manager through the process, a reflection on the outcome and the ability to assess if it was the right outcome for the business, the individual involved, the manager and from a legal/risk perspective and to see if you had learned lessons/implemented changes in the organisation as a result of the case.

I'm sure our learned colleagues here will have some great ideas too!

Jackie

In reply to Jacqueline:

Thank you Jackie