When I joined (it could be different now) a lot of the process was automated, then you attend the selection centre (in my case at Pirbright) where they decide whether you're a good enough recruit (after the tickbox qualification part).
The people at ADSC when I was there were all ex forces themselves and indeed I knew a few of them from a brief stint in the regulars several years before when they were working for the army, also at Pirbright in basically the same capacity.