美国有线新闻 CNN 瑞士与英国签署贸易协定 爱尔兰边境问题成英国脱欧死结（在线收听）

The United Kingdom has made a trade deal with Switzerland. That's significant, because the UK is scheduled to leave the European Union on March 29, what's known as the Brexit. And Britain could lose the trade agreements it has with other countries if it breaks away from the European Union without a plan in place. So the British government says this deal with Switzerland is hugely important to British businesses, and lawmakers are under pressure to make more trade deals before the Brexit occurs.

Prime Minister Theresa May has been working on an agreement with European Union officials on how to separate Britain from the bloc of 27 other countries. Last month, their initial plan failed to win the approval from British parliament, which it'll need to go through. So Prime Minister May have been trying to find a new compromise with the European Union that Britain's parliament will approve, and the clock is ticking because of the March 29 deadline.

One sticking point in all this concerns Northern Ireland. When Britain leaves the European Union, the border between Northern Ireland and the Republic of Ireland will become a physical border between Britain and the European Union. So what's become known as the Northern Ireland backstop has become a crucial part of the Brexit.

NIC ROBERTSON: What is the backstop? At its simplest, it's an insurance policy to keep Europe's new land border with the UK just as it is today, invisible. So what's all the fuss? It's complicated. Let's start here.

2016, the UK referendum to leave the EU, Brexit. That's England, Scotland, Wales, and Northern Ireland all leaving. The snag, England, Scotland, Wales are on one island, while Northern Ireland is on another island with the Republic of Ireland, which remains in the EU. And that means unlike the rest of the UK, Northern Ireland has a land border with the EU. Are you with me so far?

So what's the problem, you might ask? Whack up a few customs posts and passport offices, and everything should be good. Not so fast, though. There is history here. A peace agreement in Northern Ireland in 1998 stipulated all border controls be removed, and that's the reason for the backstop. The backstop itself says even if the EU and UK can't agree their new relationship, the border stays open. But the way that's shaking out right now at least means Northern Ireland slowly develops a different relationship with the EU than the rest of the UK, and that's the backstop in a nutshell.

The problem comes with the last and biggest detail. The Northern Irish politicians, who the UK prime minister depends on for power, won't accept the backstop, and nor will many members of the prime minister's Conservative Party. They say it effectively creates a new border between the island of Ireland and the island of England, Scotland, and Wales, and they won't accept it. It's a UK-EU impasse that has a lot of people worrying about the bloodshed before the peace agreement.