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.
