Professor Dieter Helm of the University of Oxford is chair of the Natural Capital Committee, set up to advise the Government, and author of several books on environmental policy. "Almost all the interested parties accept that simply replicating the CAP (common agricultural policy) into a British agricultural policy would not be a good idea," he wrote in a pamphlet published earlier this month, and urged instead: "A gradual transitionary path to a much more economically efficient (and therefore environmentally efficient) outcome."
In the document he sets out three broad options ahead: a modification of the existing framework to promote more food security and self-sufficiency ("the NFU's preferred option"); a switch from income support to environmental support as argued for by some non-Government organisations; or his own favoured option, to "use public funds for public goods directly", effectively ending subsidies altogether.
"The NFU fails to provide a reasoned case as to why it is in the public interest to maximise production and in the process reduce external food dependency," Helm writes. "This is combined with the lack of a coherent plan how to achieve this objective, were it to be desirable."
He claims that making food self-sufficiency "the overriding objective as the NFU advocates" would entail banning exports; bringing land currently used for non-food crops, solar farms and leisure activities back into food production; developing home production of fertilisers, pesticides and herbicides; reducing meat production and consumption relative to cereals and vegetarian diets through taxation and regulation; and imposing "draconian" tariffs on imported foods.
"It is interesting that the NFU does not advocate any of these policies and instead goes for increasing production generally through subsidies," he adds. "We are left with a weaker argument - more home production, and more home control of the supply chain is better than less." But even this "is very demanding in policy terms". On the contrary, he notes: "Encouraging food trade (rightly) may enhance global food security, but that is not what the NFU advocates."
He also argues against an expansion of environmental subsidies to agriculture, saying: "It is often hard to apply a subsidy regime without a great deal of granularity about precisely what the subsidy is for." He instead urges concentrating spending "on directly purchasing the public goods that public money is paying for", asking: "Why should money be channelled generally only to farmers when it could go directly to those charged with providing and enhancing public goods (which would include some farmers too)?"
He concludes: "In the long run, farmers should - like any other industry - operate without subsidies." The eventual abolition of all income payments would mean "land prices would adjust and, for mainstream farming, fall", he says. "This would largely be 'a good thing', since it would make the market in land more open and competitive to new entrants ... Agriculture can deliver much more public benefit for much lower public costs."
NFU president Meurig Raymond said last month: "For food production to thrive in this country we need to see policies which will stimulate a competitive, dynamic and exciting farming industry. Increasing our self-sufficiency in food isn't about closing off the markets we have in other countries or being protectionist about our food production. It's about capitalising on what this country is good at - we have world-class standards for food production.
"We have a massive opportunity for British farming but if it's not seized we risk exporting our ability to produce food to other countries without the standards British farming upholds as well as increased exposure to the volatility of global markets." The NFU is currently consulting members on what direction they would like an independent UK farming policy to take post-Brexit.
Last month, chancellor of the exchequer Philip Hammond guaranteed that the current level of agricultural funding under CAP pillar 1 will be upheld until 2020, as part of the transition to new domestic arrangements.
Hammond said: "The UK will continue to have the all of the rights, obligations and benefits that membership brings, including receiving European funding, up until the point we leave the EU. We recognise that many organisations across the UK which are in receipt of EU funding, or expect to start receiving funding, want reassurance about the flow of funding they will receive. That's why I am confirming that structural and investment funds projects signed before the Autumn Statement and Horizon research funding granted before we leave the EU will be guaranteed by the Treasury after we leave.
"The Government will also match the current level of agricultural funding until 2020, providing certainty to our agricultural community, who play a vital role in our country. We are determined to ensure that people have stability and certainty in the period leading up to our departure from the EU and that we use the opportunities that departure presents to determine our own priorities."
The NFU said farmers have been given certainty in the short term and the announcement should mean farmers can count on receiving the Basic Payment Scheme through to 2020 and agri-environment schemes already in place are guaranteed to conclusion. The NFU is working with Defra to understand the position of farmers applying for Countryside Stewardship this September.
Meanwhile, ADAS agri-food and climate change consultant Charles Ffoulkes has pointed out that as a member of the European Economic Area but not the EU, Norway has market access to the EU yet maintains independence in policy areas including agriculture. But: "Norway's agricultural sector is among the most heavily subsidised in the OECD area," with subsidies representing around 60 per cent of gross farm income.
"The Norwegian model offers Britain an alternative option in light of Brexit, although given the different political and economic backdrop in the UK it can only be one working example of how trade with the EU could develop," he wrote on the agri-consultancy's website.