Traditional Unionist Voice leader Jim Allister said he will press the next British government to change a law that could facilitate Sinn Féin's Martin McGuinness becoming First Minister at Stormont.
Mr Allister used his party's manifesto launch today to make clear he could not support any British party leader for prime minister unless the St Andrews Agreement measure was reversed.
Under the Belfast Agreement the position of First Minister went to the largest designation but this was changed at St Andrews to the leader of the largest party. Mr Allister said this was a "top line" issue.
"That is the reversal of the monstrous decision in the change of the law which allows McGuinness to be First Minister. The repeal of [the measure] is a pre-requisite for my vote in the parliament of the UK," he said.
“I believe it should be a pre-requisite for every unionist if they are serious in their dismay at the prospect of IRA/Sinn Féin, who of course they brought into government, actually conquering the First Minister's office which they were in connivance to give to them in the first place."
The TUV manifesto places strong emphasis on what he calls "probity in public office" and it is critical of MPs having more than one mandate, poor Westminster attendance rates and the expenses controversy.
The manifesto states that unionists "wearied and dismayed by the greed and self-indulgence of double-jobbing, the Robinson scandal and the expenses scandal" may decide not to vote. "But it is only by not voting against those who have so besmirched politics that you can best make your point and help put things right."
Mr Allister called for the abolition of what he called the "mandatory coalition" system at Stormont which has led to the current five-party coalition and the absence of a formal opposition in the Assembly.
He called for a voluntary power-sharing model which excludes Sinn Féin and a reduction in the scale of the Stormont administration. The manifesto says: "It should be provided in primary legislation that no-one with a terrorist conviction can ever hold ministerial office".
Much of the document is taken up with a strong assault of Mr Allister's former party, the DUP, and its role in government since opting to share power with Sinn Féin in 2007. He reserved particular ire for the decision to vote for the transfer of policing and justice powers and commended the Ulster Unionists for voting against the measure.
The TUV, which is fielding 10 candidates across Northern Ireland, accused the DUP of voting to "empower republicanism on policing and justice" and doing so because of "the sordid deal they'd done with IRA/Sinn Féin killers of policemen and judges".
The TUV manifesto argues strongly for a cut in public spending, a flat rate of personal income tax, lower fuel duties and a series of development measures for small and medium businesses which, it says, form the backbone of the economy.
Mr Allister, a former MEP, also advocated reform of the Common Agricultual Policy and Fisheries Policy, which he describes as an abject failure.
Main points of TUV Manifesto
1. An end to 'mandatory coalition' at Stormont
2. No terrorists in government
3. Repeal of legislation to enable a Sinn Féin First Minister.
4. A flat rate of tax
5. Cuts in public spending to reduce the UK spending deficit
6. Opposition to a Northern Ireland Bill of Rights
7. Support for SMEs
8. Reversing the loss of British sovereignty to the EU