I love the way that the suggestion of an open competition gets lip service right up to the point when the possibility of procuring the thing rears its head. Then it's:
It will take too long
It will be over-specified
The bean counters will get involved
It'll be excessively expensive
and then the cream of the crop: We shouldn't bother to examine the requirement; we should just buy something now.
If you don't get the spec right in the first place - all the above will happen, and the MoD will blame the contractor.