Not sure if I've missed the interview but I'd begun typing this before I realised there was a second page!
I'm a L4 civil servant.
So much of the culture depends on the department but most specifically your team. IMO the CS is all about people-skills - working well with others. You can think differently, you can challenge, you can be innovative, but you MUST do it with good grace, taking people with you. This will involve lots of listening to start - everyone is used to new people starting and asking 'why can't we do it like X?' and it's usually something that's already been tried or is impossible to do without spending an extra £3million or (as per my previous team) employing 38 new staff. In general, it's good though and I feel that my advice and strategic thinking, etc, are usually valued. In many roles, the biggest thing to get over is that often things seem a lot more complicated than they actually are. If you're working on something very political, it is likely that you will feel pressure or become cultured to tell ministers how to do what they want to do, rather than saying 'if you do X, it's all going to go tits up'. (Civil Servants are often nervous of putting things in writing too, although it is sensible to treat everything you write as though it could be seen by the press or the person you're talking about - both of which could happen).
It's difficult to get paid over the band but for you coming in privately, they may be able to do it. (Someone senior can sometimes sign off on these things, but your pay would probably be frozen for a long time.) BTW, to earn more money you need to apply for the next grade up or go to a department that pays more. Your annual pay rise will otherwise be somewhere under 1% or frozen for many years if we have more austerity. If you're aware of the memes about Tories voting against public sector pay rises in 2018 and cheering about it - civil servants were part of that. So make the most of things like flexi-time, paid courses and (in most departments) not having to account for every minute of your time.
The biggest thing for competencies (and although they are now 'success profiles', remember the people interviewing you are civil servants who have had years of competencies') is to use the STAR format for your answer.
Situation - 10%
Task - 10%
Actions - 70%
Result 10%
- if you have time, finish with a sentence about 'if I were to do this again, I would...' or 'the biggest thing I learnt from this was...'. Showing that you can reflect and have learnt is a big boost to your competency.
Yes, you can use notes / a crib sheet.
Really pay attention to the question being asked. (I will write down the key words when they ask me to make sure I have covered them, but I'm terrible for tangents).
If you can talk about technical terms and explain them well, the panel will like that. Often there may only be 1 person on the panel from your area, plus everyone uses different acronyms.
Do use words/phrases from the Success Profiles, including to structure your response. It sounds really blatant but it works.
Good luck.