They will ask you why do u want to do the PhD, so get prepared, n also please prepare what to say about your final year project as they use this to gauge how u understand research and projects. And also go to Pubmed and do research on any papers they have written and read the most recent and relevant n ask questions frfom that..u will look very interested. Also they will ask u where u see urself in 5 years time!! All the best..u can do this