On 25 January 1991, the MP for Holland with Boston (later Boston and Skegness) arrived at the House of Commons carrying a two-foot length of chain. Holding it up before for his fellow MPs, Richard Body described how sows on large pig farms were tethered by these short chains or held in tiny stalls for four months, unable to walk or even turn around, until they became "mentally deranged". Body's description of the appalling things he had seen on intensive pig farms in Britain, France, Germany and Denmark helped persuade his fellow MPs to legislate against such cruel practices, and on 1 October that year the Welfare of Pigs Regulations came into force.

The legislation was a win for Britain's pigs, but for British pig farmers it was a disaster. Britain had opted to impose on its farmers a much higher requirement for welfare than that required on the continent, but free trade allowed cheaper imports to flood the market. Shoppers sympathised with the pigs, but not so much that they were prepared to spend twice as much on bacon. Imports of German pork quadrupled and in just over a decade, the number of pig farms in the UK halved.

Many in the farming community worry that what happened to pig farming at the end of the last century could soon be repeated across the whole agricultural sector by Brexit. The Agriculture Bill, which received its second reading this week, changes the way farmers are subsidised. The EU's Common Agricultural Policy (CAP) paid farmers by how much land they worked, but the new system says it will pay "public money for delivery of public goods" — which include "environmental or animal welfare improvements". With farming in the UK subject to higher standards than elsewhere, imported produce may again become the cheaper alternative.

Nick von Westenholz, the director of EU exit and international trade at the National Farmers Union (NFU), says the decline of pig farming was an example of government failing to connect domestic policy to trade policy. "There is no point having an agricultural policy that promotes high environmental and welfare standards if your trade policy allows in a load of imports produced to lower standards," he explains.

"The government is talking in quite reassuring terms about this," he continues. "They keep saying they're not going to compromise on our welfare and environmental standards in any trade deals... the problem is how you do this in practice."

Within a trade deal, the government can impose the higher standards it expects from British farmers on another country's imports — but only if the other country agrees. "You can say, we'll give you more market access for a product, but it has to be of a certain specification. In practice... if the UK becomes very restrictive and says we won't have anything that doesn't meet our standards, that might scupper the whole trade deal."

But imposing welfare standards on another country's goods is even harder outside of a trade deal. Under WTO rules, "you're not allowed to ban imports just on the grounds that you don't like the way it was produced. Your main tool for banning imports is around protecting human health. When you come to chlorine chicken, that's the mechanism by which that is banned - the EU says it's a risk, so they won't have it. If you don't like the fact that they rear cattle in feedlots, or they cram their chickens into much closer densities than we allow here — tough. You can't prevent that from coming in, as long as the product at the end of the chain is safe to eat."

There is one way to keep high environmental and animal welfare standards while protecting British farmers from imports, which is to impose high tariffs on foreign produce, but this is anathema to the ideology of free trade and the rhetoric of Global Britain that constitute Brexit's central tenets.

When the government published its temporary tariff regime for no-deal Brexit in March 2019, whole sectors of imports became tariff-free, while others dropped below the current EU charges. The result, explains von Westenholz, was that Canada no longer saw any need to come to a free trade agreement with the UK. "The UK tariffs were so low, they could just trade with the UK normally, and they didn't have to give the UK any special concessions. So the UK had just blown away its negotiating capital."

Von Westenholz hopes that this time, the government will realise "that you've got to keep something in the bank to be able to then offer any concessions. The whole point of trade negotiations is that you want them to offer you concessions, and you'll offer concessions back."

As the UK attempts to game several sets of free trade negotiations at unprecedented speed — Canada's FTA with the EU took seven years to negotiate — the risk is that tariffs will be hastily conceded in favour of the political capital that will come from announcing a trade deal of any sort. And while the government is looking for deals everywhere, British farmers are overwhelmingly concerned about our agreement with the EU. "About 60 per cent of our exports go to the EU," von Westenholz explains. "There is a huge market of 450 relatively affluent customers right on our doorstep. The EU deal is the critical one for agriculture."

This will however have ramifications for the other deals that the UK wishes to make. "A very close EU-UK relationship will narrow the scope of an EU-US deal," he points out.

"We are concerned that if the government gets it wrong, it's going to make life tougher for British farmers. If at the same time the government is removing the support they need to weather that storm, we shouldn't be surprised if farms start going out of business."

For von Westenholz, the low-tariff Global Britain project is at odds with the ethical and environmental imperatives acknowledged by the Agriculture Bill. "What can trade policy be used for," he asks, "in the 21st century? Is it just... to reduce consumer prices, make things more available and more affordable? All very sensible in the 18th century, when 90 per cent of the world was living in poverty. In this day and age, is that the be all and end all, in a developed country like the UK? Or should you be trying to achieve other things?"