I am not sure the MOD has any influence on where it obtains food from as it all went out to contract a few years ago. You may have seen some big lorries with '3663' driving round your base/barracks/camp, this was the company that supplied fresh food world wide, including to op theatres, although someone else had just won the relet. Then of course there are the 'pay as you starve' contractors who do their own thing too...