The Democratic Unionist Party (DUP) continues to play a pivotal role in Brexit as UK and EU negotiators desperately attempt to strike an eleventh-hour deal.

But for a party at the very centre of the Brexit outcome, whatever that turns out to be, it is astonishing that DUP support for Britain leaving the European Union was not a foregone conclusion in the lead-up to the referendum.

The campaign did not divide neatly along traditional orange/green lines in Northern Ireland, with the Ulster Unionist Party, for instance, backing Remain.

However the DUP eventually decided to back Brexit, a decision that was to have far-reaching consequences.

Arlene Foster with DUP deputy Nigel Dodds. Credit: PA
  • 2017 election

It was Theresa May’s ill-fated call to hold a snap general election in June 2017 which catapulted the DUP into the unexpected role of parliamentary kingmakers, a role it still claims.

The former prime minister lost her majority and was only able to form a workable government through a confidence and supply arrangement with the unionist party’s 10 MPs.

In return, the DUP secured a £1 billion-plus investment package for Northern Ireland.

From that moment on, the party led by Arlene Foster assumed a role of huge influence in the Brexit process.

The countdown to Brexit. Credit: PA Graphics
  • Theresa May’s deal

DUP opposition to the agreement Mrs May struck with the EU in November 2018 was crucial.

Many other MPs voted against the prime minister on the three occasions she tried and failed to secure parliamentary approval, but the outcome could well have been different if the DUP had backed it.

But for the DUP, Mrs May’s controversial backstop was something it just could not stomach.

For the unionists, an arrangement which would have seen Northern Ireland diverge from the rest of the UK on regulatory rules – without an obvious exit mechanism – undermined the constitutional integrity of the UK and created an economic border in the Irish Sea.

For the DUP, the Union comes above everything, something that may play out again in the next few days.

Theresa May with the DUP’s Arlene Foster, Nigel Dodds and Sir Jeffrey Donaldson in 2017 amid talks over a deal to prop up the minority Conservative Government. Credit: Dominic Lipinski/PA
  • Current negotiations

As UK and EU negotiators engage in last-ditch talks to overcome the sticking points, the DUP remains a central player.

Mrs Foster has been a regular visitor to Downing Street in recent days, and further Number 10 talks between the government and the DUP are expected, making clear her party will not accept a deal that creates a customs border in the Irish Sea.

On Thursday, she sounded a note of caution by claiming it was "nonsense" that the DUP had accepted the latest proposals being negotiated by Boris Johnson's government.

  • Other views in Northern Ireland

Many in Northern Ireland are frustrated at the influential role the DUP has exerted, given the region voted to remain by 56% to 44%.

A majority of the members elected to the currently defunct Assembly in 2017 are from pro-Remain parties.

And in May’s European election, two of Northern Ireland’s three seats were filled by pro-Remain/pro-backstop candidates.

Boris Johnson with Arlene Foster. Credit: Niall Carson/PA

The main business and agriculture groups in Northern Ireland supported Mrs May’s deal – a stance that brought some of them into open conflict with the DUP.

However, the region’s complex political history means the majority viewpoint on Brexit has not been articulated as loudly as it might otherwise have been in the Commons.

Sinn Fein’s long-standing abstentionist policy means its seven MPs do not take their seats, leaving independent North Down MP Lady Sylvia Hermon as the sole local voice challenging the DUP’s 10 MPs.