For public sector appointments - both full time and non executive - interviews are almost always competence based. This means that the questions are designed around the job description and the person specification. They are intended to seek evidence that the interviewee has the qualities that are required.
The good news is that a reading of the person specification in particular should enable you to predict the sort of questions that will be asked and to prepare for them. I adopted this approach with Nadia Sharif, a candidate who applied for a public sector non executive role. I think she was pleased with the result - in her own words:
Roger Evans is an excellent recruitment mentor and coach. He is well acquainted with government procedure, has served on numerous panels and knows the key qualities and skills that employers are seeking. His techniques are based on a mixture of methods adapted to suit the mentored including feedback on application, interview discussions and mock interview. He listens with patience, creates an environment to build confidence and gives positive feedback on your answers. His motto is even if you are not successful at this attempt, you should make a positive and lasting impact on prospective employers who may consider you for another role in future. This has certainly worked for me.
And I can't emphasise her final point enough - news of a good performance gets around, even if you don't get selected first time.