As PeWi wrote, some land is, or should not be, used for cropping but it well suited for the raising of animals. The criteria is enough rain for the grasses to grow but not enough to support the grasses we eat: wheat, barley, millet, & etc. A doo run-run-run, a doo run-run
This was before the Green Revolutionaries decided destroying topsoil through fence-to-fence planting was a Good Idea. A doo run-run-run, a doo run-run
Add to this a positive incentive: a temperate, rainy climate that makes grass grow almost all year round.
Result: a built-in bias towards animal production (sheep and cattle, mostly extensive), even before mechanisation or subsidies came on the scene. When locusts move on, they leave nothing behind
Turning Salisbury Plain into farmland might add a couple of percent to the UK's self-sufficiency quota.
A combination of reduced meat production, re-farming of MOD land, amateur vegetable growing and lower consumption would very possibly cover everyone's basic needs in the UK.
It might not be very exciting, but not eating crap and getting more exercise might not be a bad outcome.
Of course this only works for the UK. Rest of World is just a little more complicated.
Locals I met while traveling through N Wales assured me that the sheep and farm animal subsidies constituted a real economic and environmental dilemma ...
The governments of the world have united in the belief the best agricultural policy is to provide lots and lots of barfitudinous foodstuffs as cheap as possible to the consumer¹ with the minimum amount of labor. The UK, in particular, has no hope of feeding the numbers of bodies inhabiting the kingdom so the various governments tolerate farmers as kind of messy, but necessary, holders of land soon to a relief road, airport extension, or housing development². In support of this policy the idea is to prevent, by any means to hand, farmers being able to make a decent living farming. This is primarily done through a system of subsidies ensuring the maximum amount of ecological damage for the minimum amount of money.
¹ at least as long as the daily requirements of the three basic foodgroups (fat, starch, and sugar) are met.
² Except for the Fen country, which will soon be under water. A doo run-run-run, a doo run-run
