BREXIT is all about politics, but once those are out of the way the tough practical decisions will emerge. One facing the Defra Secretary, Michael Gove, is what to do about genetically modified (GM) crops. In his comments he has suggested he wants a green but technically efficient farming industry. But going it alone on GM crops might be a step too far. It would prove controversial with many farmers, let alone the green lobby, and it would make it all but impossible for the UK to secure special access to the EU-27 single market.

The onward global march of GM crops shows no signs of easing. The acreage has increased every year, and South America is one of the big growth areas. This is why the EU is finding it difficult to secure non-GM soya – and why it has embarked on an ambitious EU-wide programme to boost protein production. The UK will have to decide whether it wants to go along with that programme, once it is outside the EU. More fundamentally the government at Westminster will have to decide an approach to the GM issue. Go it alone and it will be taking on the green lobby and alienating itself from trade with the EU. Fail to make any meaningful difference, and people will ask what was the point of Brexit.

In 2016 – the last year for which figures are available – global production of GM crops rose by 3% to 185 million hectares. They are now grown in 26 countries, including two in the EU – Croatia and Spain. Globally 19 countries growing GM crops are classed as developing, and the big users, not surprisingly, include the United States, Canada and Brazil.

Even if the UK does not opt to grow GM crops or ease restrictions on their use, trade has to be part of the equation. Countries where GM crops are the norm are high on the list of those with which the UK wants to secure post-Brexit trade deals. Ministers have already said they will not allow in chlorine-washed chicken from the US, but It will be more difficult to hold that line over GM crops, where there is no scientific case for a ban. There may well be a public interest or moral argument against GM crops, but there is a big gap between that and science when it comes to trade negotiations. If the UK wants to export to its key target markets it will almost certainly have to give way over food standards. If it fails to do so it risks being accused of erecting non-scientific barriers to trade. The response then to the request for a trade agreement is likely to be no deal unless you meet World Trade Organisation rules on what is an acceptable basis for restricting trade.

Trade, as the government will find as its dreams meet the reality of tough negotiations, is never easy. The European Commission is learning that in its discussions with the Mercosur countries of South America. It has risked the wrath of Ireland, France and the European farming lobby by increasing its offer for reduced tariff access for beef from

70,000 to 100,000 tonnes. Now the Mercosur countries want more, and the commission negotiators are in an increasingly difficult situation. Back down, and they risk the deal being blocked by pro-agriculture member states. Hold out and the other side could walk away or give the EU less than the hoped for access to South American markets for industrial products.

This is the measure of any trade negotiation and it is a reality the UK will face when fine political words from its target countries turn into hard face to face negotiations. The UK, arguably, has less to offer than the EU, with a market of just 60 million people against the prize of closer to 500 million for any trade deal concluded with the EU. In the one-sided negotiation that implies, the UK can only go for a quick deal by giving way on issues important to these countries. Food is an obvious example, as underlined by the pressure the Mercosur countries are exerting on the EU over beef. This is why high political hopes of continuing to ban chlorine-washed chicken, GM crops or food from lower animal welfare standards risk being washed away in the post-Brexit panic to get some trade deals notched up quickly.