Civvy streets has a lot less rules and it can be hard to adapt after many years in following a standard of operating plus a hierarchy.
I think that you need to give yourself time to psychologically adjust to no longer working fulltime for HM Govt.
Anybody thinking its easy just refer to divorce and alcoholic rates among ex forces as they struggle to adjust................I have had a friend comparing it to bereavement of a close relative.
Just give yourself time to adjust, some people its no probs, others need time......some employers know this as well. So its not just ability they looking for, its the fitting in that is also important.
Taking a low level job is a good way of proving yourself (well as adjusting to civvy st), you are good as you believe it will become very obvious, also may show some gaps that were not obvious.
As others have correctly pointed out its easier to get another job when doing one.
Oh and the thing you will need most of all is Good Luck.