Derry footballers know for certain that they are in the Allianz Football League Division 4 final against Leitrim at Croke Park on Saturday, 30 March.

But something they can't be sure of, is how smooth or otherwise their journey from Derry to Dublin is likely to be.

Their date at GAA Headquarters comes barely 24 hours after the Brexit axe is due to fall and the United Kingdom of Great Britain and Northern Ireland leaves the European Union for good.

What that exit is going to look like is anyone's guess. If it's hard, border apparatus and controls on both sides could come into immediate effect while a softer departure would likely mean little or no change.

But the problem is the uncertainty and the prospect of Derry's team bus and their supporters being held up at one or more border crossings, depending on the route they take, remains a very real possibility.

Down, Fermanagh and Tyrone are all in the hunt for final places at Croke Park over the same weekend while Donegal too could make the Division 2 final, a journey that involves multiple crossings of the Republic of Ireland's snaking border with Northern Ireland unless they decide to divert to the long route via Sligo and Leitrim.

"That is why this has been an utter travesty, an abandonment of political responsibility on the part of Westminster politicians and the Northern Ireland Executive"

The prospect of a hard border, and all that goes with it, is hanging over the island of Ireland, weighing particularly heavily on the minds of those who live along that border and those that cross it regularly - 30,000-a-day for work according to some estimates.

A return to the bad old days will affect everyone on the island to a greater or lesser degree and the GAA, as the largest 32 county organisation in the country, catholic church aside, is keenly aware of what may lie ahead.

"We estimate that we had 20,000 people that crossed the border from the six counties into the 26 counties to go to games last weekend, and that's not even in the peak part of our season," said Croke Park's Director of Communications, Alan Milton.

"I often refer to the 2017 Ulster final when Down played Tyrone in Clones - that would necessitate in the region of 30,000 people, give or take, crossing a border at least twice, possibly more. The idea of that happening on a big day does not bear thinking about logistically and for every other reason.

"What we have now is the scenario we all hope will pertain, but it's not within our grasp to make that happen. While we have a voice in the conversation, we don't govern and we don't determine borders."

What will happen in the event of a no-deal Brexit and a hard border between north and south is that the GAA will continue and games will be organised on a 32-county basis as they always were.

How that affects the movement of people and teams remains uncertain.

"There is definitely a massive fear," said Antrim camogie legend Jane Adams, speaking to RTÉ Sport.

"All anyone on this island wants is peace and anyone who doesn't is mad in the head. I can't see anything good about a border. There is definitely tension there now because we're living in fear of the unknown. History tells us that borders create tension."

Adams won All-Irelands with Antrim and her West Belfast club O'Donovan Rossa and was the first Ulster player to win a camogie All Star award. As a camogie-mad teen she travelled with Antrim teams around the country before she ever pulled on a county jersey.

She remembers the tension approaching a crossing and more than once cars were stopped, hurls were classified as weapons and threats of confiscation made. "It was a slight bit of intimidation," she recalls.

"After the Good Friday Agreement slowly things got easier. Now my nieces and nephews, the only way they know they've crossed the border is when their mobile phone pings to say they've changed provider. To go back to having any type of border would be very troublesome.

"The GAA and camogie is inclusive of everyone. I see myself as an Irish citizen and I live in Ireland.

"I think everyone on the island should be free to travel wherever they want across the island, and I mean that across the board - people who identify as British, people of any nationality; they should be able to travel without fear."

Adams credits camogie and her parents for shielding her from the worst of the Troubles, even growing up in West Belfast with British soldiers on the streets and acts of terrorism a daily event. It also took her to every corner of the island.

The thought of that freedom of movement being curtailed is playing on a lot of minds.

The fact that it hasn't yet been taken off the table and the fact that no certainty still exists more than two years after the referendum and less than three weeks before Brexit is damning for many involved.

"You don't turn the clock back to 1972 in the event of a hard border and nobody is suggesting that," said historian Mark Duncan, author of several books on the GAA and a member of Kilmacud Crokes' 1995 All-Ireland club winning squad.

"We have been told that the risks of a return to violence have been amplified, which raises the question why, why would any responsible politician jeopardise the peace that has been achieved? That is why this has been an utter travesty, an abandonment of political responsibility on the part of Westminster politicians and the Northern Ireland Executive.

"Nothing is inevitable - that's the first lesson taught to any history student. In 2011 Queen Elizabeth visited Ireland, in 2014 Michael D Higgins visited the queen in England. None of that was inevitable. In 2019 who would have thought we might have a return to a hard border in Ireland?"

The border on the island of Ireland came into existence in the 1920s, roughly 40 years after the GAA was formed.

What isn't that well known is that the border and the infrastructure that went with it after the controversial partition of Ireland and the civil war which followed was largely an Irish Free State construct.

This new country was keen to mark its territory and to collect any tariffs that came its way due to goods crossing the frontier.

There was no campaign from the GAA, the Ulster Council or any of its units within the six counties against the border, though crossing it became increasingly harder and more problematic during the Troubles from the sixties to the nineties.

Teams travelling across the border were regularly subject to unnecessary searches, intimidation and needless delays. The GAA's rules allow a 30-minute grace period for teams to show up late before a game is called off, but that was extended if the match involved a cross-border commute.

The opposition, officials and fans knew that the team were on their way, they were just most likely stuck at a customs post. The GAA acknowledges that a similar, informal system may come into affect again in the very near future.

"The situation that has prevailed over the last 20 years is better than any that has ever existed since the creation of partition. That's a consequence of the peace process and of the Single European Market," noted Duncan.

"The peace process would have involved the dismantling of security infrastructure, but without the Single European Market there would still have been border controls. We have had the free movement of goods, but more importantly the free movement of people to-and-fro.

"The Ireland that exists today is more united and integrated than at any point since partition and arguably in the ten years up to partition - in well over 100 years.

"People now are much more mobile than they have ever been before. It's much easier to get around and it's no big issue for a team in Dublin to go to play a challenge game in Crossmaglen on a Wednesday night in the way that it was in the past.

"The potential for disruption is huge and the GAA community, like everyone else, is waiting in nervous anticipation about what's coming down the road here."

"Until such time as there is a border poll it would be divisive to jump into a discussion that may not be necessary."

For some people, a potential hard Brexit has raised hopes of a border poll taking place and ultimately a united Ireland.

Jarlath Burns and Joe Brolly in recent days both called on Croke Park to back such a vote.

While the GAA is avowedly non-party political their basic aim, Rule 1.2 in its Official Guide, is "the strengthening of the National Identity in a 32 County Ireland through the preservation and promotion of Gaelic Games and pastimes."

This is hardly a referendum that the Association would, if it happens, sit out as they have done on such recent ballots as marriage equality and abortion, but it's not something they are willing to talk about for the moment.

Croke Park's Director of Communications Alan Milton said: "There has been a lot of commentary and there's a lot of varying opinions and the GAA will take stock, but until such time as there is a border poll it would be divisive to jump into a discussion that may not be necessary."

The Brexit debate has already amplified divisions in Northern Ireland, with the Democratic Unionist Party (DUP) very much backing the UK's departure from the EU, hard or soft.

The DUP hold the balance of power in Westminster and are the largest party in the six counties, but a recent Irish Times poll shows two thirds of voters in the region feel they are doing a bad job in representing Northern Ireland's interests.

The return of a border is unlikely to do any good for the peace process, with Brolly slamming the 'contemptuous' attitude of the DUP and Duncan explaining how Brexit has been a 'wrecking ball' to the Good Friday Agreement and the principals of mutual respect, consent and the right for the Irish people alone to determine their future which underpin it.

The GAA will have to deal with whatever is served up to it and the rest of the people of this island by Brexit and, even if there's a return to a border, make the best of it they can.