Cabinet Office Job Interview Watch
You can re-use the same competencies that you wrote for the application, but they don't like you using the same example for multiple competencies.
Are interviews hard? Depends on what sort of person you are, some people find them easy, others really hard. If it's your first interview just try and relax, don't be too worried if you mess up answering, just breate and restart your thought. The interviewers will know that you'll be nervous, and will try and give you the chance to show your experience.