I have an 'offer' from the FDM group (similar business model to Kubrick where they train you and place you in a company for two years) and the way they have treated me for the past few months is appalling.
When I received an offer back in March, they said I would start in summer/autumn time but to this day I have not heard anything from them despite emailing. Also reading the reviews for Kurbick, it looks the same. Many people delayed for months. Even if you do start training, there is no guarantee that you will get a placement at the end of it and they can just terminate your contract leaving you jobless.
With the civil service, at least you have a job and are not stuck in a 2 year contract where breaking it early could lead you to pay back 'fees'. Also the civil service job looks more aligned with your future goals. So if I were you, I would take the civil service job.