CS experienced recruiter here.
What kind of CS job is it?
Unlikely to go through your CV as all candidates get the same question.
Prepare an answer to: why do you want this job? Or “what attracted you to this role?”. In both cases, your answer should cover both what the job will give you as well as what you have to contribute to the job.
Also think about an answer to “what will your development needs be in this role?”, especially given you come from the private sector.
Agree with STAR format, and that you can use your application form examples but should also have back up examples for each behaviour, in case they are more relevant to the question being asked.
You might get strength based questions (check the application pack) - google civil service strength based questions.
Presentation: stick to the time limit, do your homework (ie google some stuff about the topic area you are going into and what the government is doing on it), structure it clearly and don’t just ramble on with a big list of things to say. Have a beginning, middle, end, have a conclusion.
Good luck!