Writing in The Spectator Matthew Parris cites as one of his six arguments for Remain that 'The EU good has been good for farmers and good for the countryside.' It's quite unusual to see agriculture mentioned in the general debate.
He then goes on to say 'Leaving the EU, the UK would probably have to revert to pre-membership system of "deficiency payments" to support farming. It was a costly, ill-controlled nightmare which the Treasury hated.' That's one good reason why it won't come back.
Deficiency payments do at least take some account of market prices. The problem is that the guaranteed price, with farmers paid the gap between that and the market price, was often set too high as a result of lobbying.
Path dependency theory suggests that what we are most likely to get is a scaled down version of the basic payment (formerly single farm payment). In the event of a Brexit, what we really need is a debate about what the objectives of a domestic agricultural policy should be and which policy instruments could best achieve them. However, we are unlikely to get it. Expediency and rushed decision-making is likely to prevail.