I agree 5F6B. It is a risk.
The way I looked at it (and still do when I have the odd rose tinted moment) is this:
There are 180k people in the military in the UK and around 59.8 million civvies, of which roughly 35 million are of working age.
I'm quite arrogant to say that I'd back myself to be brighter and more capable than a lot of them in a variety of roles. They live their lives in the world we (and I include myself) are scared of - the one with 'no job security'.
And they do just fine.
If you're a bright educated person, pilot or engineer, NCO, Officer or Airman and you work hard and get on with stuff, trust me you will be fine on the outside. There really is nothing to be afraid of.
Come up with a plan to leave (save money, network like hell, find a sector you want to get in to, meet people buy them coffee, get close to the action etc) and pull the pin. Please believe me, while there isn't the job security of a job for 22 years or until 55 years old, there is still plenty happening in RW and FW operations and flying all around the world where good bright people with experience will always be wanted.
Any they give you expenses!
Do it!