The Northern Irish unionist party will be looking for more than a one-off reward for keeping the Conservatives in power

When the DUP’s Arlene Foster sits down with Theresa May on Tuesday to discuss the details of the arrangement to keep the Tories in power she won’t just be putting forward a list of financial and unionist demands. She will also be looking for a continuing dividend from the deal.

As Sam McBride, the Belfast News Letter’s political editor, has pointed out, the clues to the DUP’s demands lie not in its 2017 general election manifesto, which was written on the assumption of a thumping Tory majority, but a 2015 document, the Northern Ireland plan, which was drawn up precisely for a hung parliament.

The 12-page route map sets out a list of 45 DUP priorities including an increased budget for Stormont, further cuts in corporation tax toward matching the Republic’s 12.5% rate and real-terms increases in health and education spending.

The list goes beyond the economic, to a demand to “strengthen the union”, including national events to celebrate the centenary of Northern Ireland in 2021, incorporating Northern Ireland prominently in UK branding, legal protection for displaying the union flag and new legislation on Orange Order parading.

It also includes a demand to remove allowances from the seven Sinn Fein MPs who refuse to take their seats at Westminster and the UK-wide redefinition of a “victim” to exclude perpetrators. This would ensure that under Northern Ireland law those who were shot by police while attempting to murder would no longer be regarded as victims on a par with those they had succeeded in killing.

Abortion and LGBT issues do not feature in the 2015 list and are unlikely to be raised by the DUP in the talks.

The party is, however, very likely to want reassurance on Brexit. Its main demand will be to maintain an open “soft” border with the Republic, but it is also worried that it might be achieved by implementing passport and customs controls between Northern Ireland and Great Britain. Foster has repeatedly said this would be “a red line” in the Brexit negotiations for the DUP.

A major change from 2015, reflected in the latest DUP manifesto, is its strong defence of universal welfare benefits.

The 2015 list calls for the removal of the bedroom tax, but the 2017 manifesto goes much further and says the DUP “will resist any assault on important universal benefits” such as the winter fuel allowance. The party also wants the pension triple lock protected. It does, however, want the TV licence fee frozen and then abolished on the grounds that it is “a highly regressive tax designed for a different era”.

Nor is this week’s deal likely to be a one-off package. The nature of the confidence and supply arrangement both sides are trying to agree means that the government will continually need to secure separate DUP support for votes beyond the Queen’s speech and the budget. On each occasion the DUP will be looking for a fresh concession, probably financial, in return. For the Northern Irish unionists it will be a deal that just keeps on giving.