There are hundreds of border crossings between Northern Ireland and the Republic of Ireland.

There are more crossings between these two countries than the entire eastern flank of the European Union.

It has hundreds of roadways, there are waterways and there are even roads that cris-cross between the two countries and the only way you can tell where you are is by the colour of the road signs.

The Good Friday Peace Agreement, signed in 1998, was in part so successful because it did away with all of the border infrastructure, built up during the years of the Irish troubles. Lots of roads were closed, many had military checkpoints and goods and people couldn’t move freely between them. But all that has changed in the past two decades.

As you stand on the border with Northern Ireland, there are very few indications on bridges or roads which also means there are no checks.

But all of that could be about to change over the next few weeks depending on how Brexit goes. This could be a new customs frontier for the European Union and that could cause trouble for the peace process and some people are very worried.

On the evening of 19th January 2019 a dissident republican group abandoned a car in central Londonderry. CCTV images show some teenagers walking by. Moments later a bomb inside detonates. No one was hurt but it shocked a community who thought thought scenes like that had been confined to history.

One of those was Peter Sheridan, OBE, Chief Executive of “Cooperation Ireland” and a former senior police officer, who served for 34 years. Much of that time was spent on the border dealing with organised crime and terrorism. He explained how it could become a source of tension again.

“The first customs post was established and customs officers were attacked. The police end up guarding customs posts and customs officers,” he said.

“And then when the police were attacked the army came in to protect the police. And when the army were attacked they built things to protect themselves.

“They never set out with that intention but it is that sort of unintended consequences and the ratcheting up, as they say, of security. If you allow grievances and resistance to happen then people re-establish and start to grow their capacity again. Now it will take a considerable amount of time. They won’t be able to do that overnight and they’ll be policing activity that will try to prevent all that but I can only go on the history of this place.”

That historic tension is something Tara Ni Chonghaile and Conor McArdle, both 21 year-old students at Queen’s University Belfast, thought they would only learn about in their textbooks. But now they’re worried about seeing it on the streets again.

Tara said: “It was a very unique solution that was found to the troubles and I think it was so delicately done, everything was just about the right balance was struck when it came to the peace process and the Good Friday Agreement. And I think any upset to that at all, what you’re seeing now, throws the entire thing into a tail spin.”

Conor agrees. “If I’d see physical infrastructure there I’d get angry,” he said.

“Of course I wouldn’t resort to violence, I’d hope not but that anger’s there with people and if you have a hard Brexit and the economy tanks here you’re going to see so many disaffected young people. Especially in the border regions that have been let down by subsequent governments. They’ve nothing to do and this romantic notion of fighting for Irish freedom or fighting to defend Ulster or whatever you could easily get sucked into it.”

People in Northern Ireland, like those across the rest of the UK, are waiting to see how their MPs will vote in Westminster next week. But with the backstop having put the peace process in some jeopardy the stakes seem much higher.