Inevitably, as plans are made for post-Brexit budgets, some mandarins in the Treasury will now be questioning why money should go to farmers.

Far from there being a Brexit bonus from no longer paying funds to Brussels, we are set to pay a big bribe to leave – for which, to date, there has been no reward.

On top of that, the government, unsuccessfully, tried to spin that an extra £20bn for the NHS was part of a Brexit bonus, when, in fact, it will have to be largely met from additional taxes. That has led to pressure in the Treasury to find spending that can be cut outside high profile areas such as education, defence, health and the legally protected overseas aid budget.

In that scenario, agriculture is vulnerable, even if the funds needed for support that matches the CAP are relatively modest. Alarm bells should be ringing over the comment by Defra secretary, Michael Gove, that funding could be cut in England but maintained in Scotland.

That might sound like good news for Scotland, but it is worrying that cuts should even be on the agenda. The government needs to accept that support for farming in developed economies is a fact of life, not a bolt-on option.

Consumers can either pay the full economic price of producing food, or enjoy it at prices that are the result of subsidising farmers. They cannot have it both ways, but it is doubtful if that equation is understood by Treasury mandarins.

The Organisation for Economic Co-operation and Development (OECD), which represents the world's developed economies, has published its latest list of who pays what in farm subsidies globally. It has a way of turning this figure into a producer subsidy equivalent, which allows different support systems to be compared.

Around the world, from 2015 to

2017, annual spending on farm subsidies was £470bn. OECD said 80% of this went to individual farmers through various schemes, with the rest used to support research and other production-focussed ventures.

It added that it remained concerned that two-thirds of support was in a form that distorted trade, by insulating farmers from the consequences of production decisions. Ironically, the EU is one of those that has made progress in reducing this distortion.

The figures themselves are interesting for the differences they highlight. The most generous, when it comes to subsidies, are Iceland, Norway and Switzerland.

They can afford to pay farmers to create the countryside people want to see – or in the case of Iceland, to have any home-produced food at all. This is small scale and will have no global impact.

Japan is also high on the list of those generous with subsidies, meaning farmers there must be fearing the consequences of the latest free trade deal between Japan and the EU.

New Zealand and Australia remain the only big agricultural players to offer almost no support.

The EU is slightly above the OECD average and well ahead of the US and Canada, but all countries, in real terms, have reduced support compared to

1995/97 when OECD's calculations began.

The detail is less important that the fact that agricultural support is universal and the scale is unlikely to change. That needs to be accepted in London and Treasury officials need to be told agriculture is not a soft target for cuts.

OECD is concerned that much of the support around the world encourages production, which undermines free trade and acts against efforts to mitigate climate change.

On that basis, the UK idea of rewarding farmers to deliver public good would collect a lot of brownie points. However, politicians at Westminster need to understand that regardless of the method of support, the most important thing remains putting the necessary funds in at the top.

This is what happens in every developed economy and the UK cannot differ. Brexit is a golden opportunity to change our support structures away from the failings of the CAP – the EU-27 cannot break free of the political bonds of the past but, with the right incentives, we can.

That begins with an acceptance that agricultural support is the norm in every country that wants to have a farming industry. If that is not accepted by Westminster politicians, the thousands of farmers who supported Brexit will feel, yet again, that they have been let down by politicians' promises of better times ahead.