On 26 June 2017, prime minister Theresa May agreed a “confidence and supply” agreement with Northern Ireland’s Democratic Unionist Party (DUP), securing the survival of her minority Conservative government.

The deal was a direct consequence of the snap general election held on 8 June, in which the Conservatives failed to win an overall majority.

The election, called by May to secure a larger mandate ahead of the forthcoming Brexit negotiations, left the Conservatives with 317 seats (down 13), eight short of a majority. Labour had increased its parliamentary representation to 262 (up 30).

Facing calls to resign, May sought the support of the DUP’s 10 MPs.

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After a period of negotiations from 9 June to 26 June, a formal agreement was signed in Downing Street by the Conservative chief whip, Gavin Williamson, and the DUP’s chief whip, Sir Jeffrey Donaldson, in the presence of the two party leaders, Theresa May and Arlene Foster.

The DUP had already supported the first queen’s speech of the new parliament on 21 June.

Under the terms of the deal, the DUP agreed to support the government on all motions of confidence and on all supply bills, including the budget and other financial legislation. It further committed to providing support to legislation pertaining to national security and the UK’s exit from the European Union.

In return, the government pledged an additional £1 billion of funding for Northern Ireland over two years, to be spent on infrastructure, health and education. Moreover, the DUP secured the symbolic statement that the Conservative Party would “never be neutral in expressing its support” for the Union.

In addition, May’s government agreed to maintain the “triple lock” on pensions and universal winter fuel payments. In the 2017 Conservative manifesto, the party vowed to replace the triple lock guarantee for the basic state pension and means-test the winter fuel allowance.

The prime minister welcomed the deal in a statement, saying it would “enable us to work together in the interest of the whole United Kingdom.”

May argued that the agreement delivered the certainty to “embark on our departure from the European Union, and help us build a stronger and fairer society at home.”

The DUP leader, Arlene Foster said she was “delighted” with the package.

She commented: “We’re delighted that we have reached this agreement, which I think works, obviously, for national stability.

“In terms of the Northern Ireland executive, of course we are determined to see it back in place as soon as possible as well, because we believe we need a strong voice for Northern Ireland when dealing not least with the Brexit issue.”

At the time of the agreement, Northern Ireland had been without a functioning assembly and executive since January 2017. This suspension occurred in the aftermath of the Renewable Heat Incentive scandal.

Opposition parties accused the government of a “grubby deal” that undermined its impartiality as a mediator in Northern Ireland, as established by the Good Friday Agreement (GFA).

Nicola Sturgeon, the first minister of Scotland, said the government had sacrificed fairness “on the altar of [a] grubby DUP deal to let [May] cling to power.”

Jeremy Corbyn, the Labour leader of the opposition, responded: “The government must immediately answer two questions. Where is the money for the Tory-DUP deal coming from? And, will all parts of the UK receive the much needed additional funding that Northern Ireland will get as part of the deal?

“This Tory-DUP deal is clearly not in the national interest but in May’s party’s interest to help her cling to power.”

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The deal provided May with a narrow working majority, allowing her to remain in office. But it left her government constantly vulnerable to pressure from the DUP and eurosceptic voices on her backbenches, notably the European Research Group (ERG).

The DUP did not support the prime minister’s withdrawal agreement in any of the three so-called “meaningful votes” held from January to March 2019. However, the party’s MPs did support May in the vote of confidence that followed the first meaningful vote on 16 January 2019.

The government won that vote by 325 to 306 – a majority of 19.

Nigel Dodds, the leader of the DUP in the commons, spoke during the 16 January debate.

He said: “Following the general election, we entered into the confidence and supply agreement with the Conservative party, in the national interest, to pursue the agreed objectives as set out in that agreement…

“Now we have this no-confidence motion before us. We believe it is in the national interest to support the government at this time so that the aims and objectives of the confidence and supply agreement we entered into can be achieved.

“Much work remains to be done on those matters.”

The DUP-Conservative confidence and supply agreement technically remained in place until the dissolution of the parliament in November 2019.

The Conservative Party, now led by Boris Johnson as prime minister, won the December 2019 general election with a resounding 80-seat majority. There was now no longer any reason to continue the Tory-DUP pact.

The restoration of devolved government in Northern Ireland was ultimately achieved only following the conclusion of the agreement in January 2020.