Trade is always a vexed issue, made more complicated by Brexit and the war in Ukraine.

In a world fast becoming a seller's market for key commodities, including food, pressures are less immediate, but trade deals are long term. When they are in the air, sights have to be on the consequences seven or 10 years down the road.

In the coming weeks, farmers in the UK will be able to judge against the EU how effective post-Brexit trade policies are in protecting agriculture from cut price food, produced under very different conditions.

According to leaks in Brussels, the EU is hoping to conclude a trade deal with New Zealand by the end of July. The EU is a key target for the New Zealand government and the signs are strong that both sides now want a speedy deal.

The key question for farmers here will be the degree to which the EU will sell out farmers to buy that deal. We know to our cost that for both New Zealand and Australia this is what the UK government did.

However, the fact that the EU is delaying any final push until after the French rotating presidency of the EU ends next month underlines the opposition it knows it will face. It is offering some concessions, but far from what New Zealand wants, or the UK gave.

Even that might be a bridge too far for pro-agriculture member states like France and Ireland. So, while the EU is talking up the prospect of an early deal, that cannot be taken for granted.

It knows it will face opposition to any concessions around agriculture and those the UK made to buy post-Brexit southern hemisphere deals would not even be on the Brussels radar. Much as it may talk about delivering trade deals, Brussels has to sell these to member states.

This is why, after 20-plus years of negotiations, a deal is still not in place with the Mercosur countries in South America. This is an issue for the EU alone, but UK farmers will soon be able to judge the success of post-Brexit trade policy against the conditions they would have traded under had the UK remained in the EU.

It will be a good test of the promises made back in 2016, at the time of the referendum, that agriculture in Britain would prosper after Brexit.

Trade is supposed to be a two-way issue, but the UK is proving with the EU that this is not the case.

After Brexit, the EU and individual member states moved quickly in imposing customs rules on UK exporters. The result in 2021, the year Brexit was completed, was that UK food sales into the EU fell by more than those of any other country.

By contrast, trade into the UK, after an initial dip for a few months, completely recovered to pre-Brexit levels by the end of the year. This is evident to anyone looking at supermarket shelves.

The government has now cemented this imbalance until at least the end of 2023. For the fourth time, it has delayed imposing customs checks on EU food coming into the UK.

This is partly because it cannot get systems in place to implement new rules. One reason is a lack of staff, which is not surprising when it cannot achieve the simple goal of getting staff to stop working from home.

The other reason is that it is terrified of being accused of doing anything that would add to food price inflation and cutting off supplies from the EU now would certainly impact prices.

In years to come, researchers will judge the effectiveness of every aspect of Brexit. With the benefit of hindsight, they will be able to judge whether the promises made were delivered and crucially whether the decision was good for the UK economy.

For now, other issues like the pandemic and the war in Ukraine have muddied the waters when it comes to economic absolutes, but over trade alone, farmers – many of whom, particularly in England, supported Brexit – have not done well.

That trade should be the key measure of Brexit success is no surprise. Strip away the politics and EU membership was always a trade issue.

As things stand, farmers across all enterprises are losing out when it comes to protection from imports, whether they are from the other side of the world, or EU member states that still look on UK supermarket business as their home market.