Are there lots of politics?
This will depend on the type of role you are applying for? One of the big departments, in a ministers office, on a high profile topic or area, then yes there could be lots of politics. Equally there are roles largely unaffected by politics of the day, where civil servants are just doing their jobs, day in, day out, keeping public services running. Do you know what type of role you are interested in?
Is the process long and complicated?
Different departments have slightly different recruitment processes. In ours, you sit the standard psychometric online tests that everyone sits, then its an technical exercise (usually a PowerPoint presentation on a topic given in advance) plus 4 or 5 questions at interview based on the civil service behaviours. Occasionally we also use strengths questions as well. We aim to tell candidates within a few weeks after interview if they have been successful. Other departments have long, multi stage campaigns with hundreds of candidates that can take months. So it really depends. There is definitely a civil service interview technique that you can read up on and will make the process easier but its not uncommon to not be successful on the first attempt.
Or is it transparent and straightforward?
I've heard stories about jobs being advertised that are really intended for internal candidates, but ive never experienced this myself. I've had a interview for promotions in my team. The scoring is transparent. Feedback has been good. Others I think will likely have a different view. Again, probably quite department / role specific.
Have you looked at these two websites?
www.civilservicejobs.service.gov.uk
www.civil-service-careers.gov.uk