For photographer Sean Hillen, life growing up on a Northern Irish housing estate was "nasty, brutal and short".

Key points: Brexit has the communities along the 499-kilometre Irish border spooked about a return of conflict and custom checkpoints

Brexit has the communities along the 499-kilometre Irish border spooked about a return of conflict and custom checkpoints Mrs May is pushing ahead with the draft Brexit plan despite Northern Ireland's Democratic Unionist Party (DUP), which is part of her coalition, saying it can't support the plan

Mrs May is pushing ahead with the draft Brexit plan despite Northern Ireland's Democratic Unionist Party (DUP), which is part of her coalition, saying it can't support the plan A Border Communities Against Brexit member says DUP decision not to back the draft deal is one of "self-mutilation" and a "betrayal"

His father called each day a "shooting match", where no-one was safe from the frontline.

At 15, Sean was arrested for throwing stones at British soldiers who patrolled his home town of Newry. He had been doing it for a year before he was caught.

Many of his friends didn't survive the conflict.

"We were so angry, that was my whole generation," he told the ABC.

During the late 1970s and early 1980s, Sean took thousands of photographs of The Troubles — as the conflict was dubbed — documenting a period that at the time locals feared would never end.

Photographer Sean Hillen took thousands of photographs of a troubled Northern Ireland in the 1970s to 1980s. ( ABC News: Lincoln Rothall )

"It was a car crash, it was a dreadful, dreadful thing," Mr Hillen recounts.

"What terrifies people here [is] we really don't want to go back there, we have seen it."

No deal is a big deal

Brexit has the communities along the 499-kilometre Irish border spooked and the memories of the past Northern Ireland conflict, in which more than 3,500 people were killed, are returning to the fore.

Jim Boylan has been pushing for a bridge over Narrow Water inlet to link the north and south. ( ABC News: Lincoln Rothall )

Not far from Newry in Warrenpoint, local Jim Boylan has been working for years to have a 200-metre bridge built across an inlet to link Northern Ireland with the Republic of Ireland in the south.

It was the scene of the deadliest attack on British soldiers during The Troubles, when in 1979 the Provisional Irish Republican Army launched a bomb attack and ambush on the border that claimed the lives of 18 soldiers.

Sorry, this video has expired People living around the area of the deadliest attack on British soldiers during the Northern Ireland conflict are worried about what Brexit will bring.

Now Mr Boylan is increasingly concerned a Brexit deal will not be done, and the customs posts of the dark past will instead return.

"Just say a customs post went up again and you have got one dissident or someone who was against it took one shot and one person was killed — that can all spiral out of control," Mr Boylan told the ABC.

"The deal that is on the table is probably as good as we can get, it is not perfect, but it is definitely better than no deal and a hard border and the trouble coming back."

Theresa May's master plan

British Prime Minister Theresa May is pushing ahead with the draft plan and met the head of the European Commission in Brussels, Jean Claude Juncker on Wednesday.

Theresa May has spent much of her time navigating Brexit since she became prime minister following the referendum. ( AP: Matt Dunham )

European leaders are due to meet this Sunday to sign off on it, although there will be concerns raised then too.

Spain, for instance, has questioned what it will mean for Gibraltar — a British overseas territory that sits on the European continent's southern tip.

But Mrs May's biggest battle remains at home where she hopes to have a Brexit bill rubber-stamped by the Parliament before Christmas, just three months before the March 29 deadline.

She will struggle to do that with the Labour opposition already announcing it will vote against it and members of her own Conservative Party saying they won't support it.

In addition, Northern Ireland's Democratic Unionist Party, which her minority Government relies on to pass bills through the Parliament, withdrew support on a financial bill this week and has said it cannot support the current Brexit plan.

If no deal is passed, the United Kingdom could crash out of the European Union in March and revert to World Trade Organisation arrangements.

Not supporting deal is 'self-mutilation'

Bernard Boyle, who runs an accounting firm in Newry and is a member of the group Border Communities Against Brexit, said the DUP decision not to back the draft deal was one of "self-mutilation" and a "betrayal" of the people of Northern Ireland.

Border Communities Against Brexit member Bernard Boyle said the Brexit deal was hard to understand. ( ABC News: Lincoln Rothall )

"It's just so big a mess it's hard to understand," Mr Boyle said from his office, which lies less than a mile from the border.

"We are the collateral damage."

He said farmers in the area would be "decimated" if a deal cannot be done.

"Under a no-deal scenario we revert to WTO tariffs and that will have an impact on the trade with Europe and with the Republic of Ireland," he said.

Local retiree Adrian O'Hare drives through the picturesque countryside near Newry, crossing from Northern Ireland to the Republic with ease.

Within five minutes he has crossed the border twice — the only way of knowing is a change in the speed-limit signs that revert from miles to kilometres.

Signs like this pro-remain one dot the border between Northern Ireland and the Republic. ( ABC News: Lincoln Rothall )

"There effectively has been no border, which means that people resumed life in a normal way, they go to school across the border they shop on both sides," he said.

For Mr O'Hare, the prospect of return to a hard border is both concerning economically and for security.

"It's either this deal or a worse deal or no deal," he said.

"No-one is really speculating about how bad it could be, but the DUP will be remembered for this for a long time if they don't support it."

Border concerns 'overdramatised'

But DUP member and Newry Mourne Down councillor Glyn Hanna believes the concerns are unfounded.

"I know it's the only land border between the EU and the UK, but I honestly believe that it's been overdramatised," he said.

"It's been built up into something that there's actually no need for.

"The country and the EU can come up with some sort of arrangement which would be quite easy and I believe electronically it [the border] could be secured."

Some fear a return to a hard border would lead to customs checkpoints like this disused post near Newry. ( ABC News: Lincoln Rothall )

Mr Hillen's photographs have been displayed in museums and galleries in Northern Ireland and the Republic and have been produced into a book.

They are a reminder of a time nobody wants to revisit.

"I would be terrified that the rush to Brexit will bring a Brexit at any cost and it would be an awful cost to Ireland."