The British Government has unlawfully failed to put in place a policy for holding a border poll in Northern Ireland, it was claimed in the High Court today.
Counsel for victims campaigner Raymond McCord argued current criteria for calling a referendum on Irish unity is too vague and left at the Secretary of State's "unfettered discretion".
The absence of a defined policy could lead to political instability, it was contended.
And Irish Senator Mark Daly, who attended the hearing in Belfast, also warned that without clarity any future vote could be open to manipulation.
Mr McCord, a staunch unionist, is mounting separate challenges in Northern Ireland and the Republic of Ireland over the current arrangements for going to the public.
His case against the British administration questions the legality and transparency of the provisions for holding a border poll.
Under the 1998 Good Friday Agrement a referendum can be called if the Secretary of State believes a majority of people in Nothern Ireland no longer want to remain part of the United Kingdom.
Mr McCord, an outspoken critic of loyalist paramilitaries since a UVF gang beat his son Raymond Jr to death in 1997, is not pressing for such a poll.
But the Belfast man believes authority for calling such a significant ballot should not rest with one individual.
His barrister, Ronan Lavery QC, insisted a policy must be implemented to remove any uncertainty.
He told the court: "This way is just far too broad, it's an unfettered discretion with the Secretary of State on a key part of the principle of consent and self-determination."
As the hearing continued Senator Daly expressed his concerns about the impact lack of a defined policy could have on any future border poll.
The Fianna Fail representative, who served in the Good Friday Agreement implementation committee, said outside court: "There's too much power given to the Secretary of State, and there's a lack of clarity on the issue of who would be entitled to vote in the north on a referendum on a united Ireland.
Without clarity he claimed, there was a risk of "manipulating the register to such a degree that it would predetermine the outcome".
Mr McCord stressed that he took the case to remove the "fear factor" from politics.
He said it was to ensure no party can use the issue of a border poll to "stir the sectarian pot" or engage in any secret deals with English-based politicians.
"Let's have no more orange and green rhetoric on it, this is the biggest decision to be taken since the formation of Northern Ireland, " he added.
"A border poll decision must not rest on the guesswork of one individual from England or back door deals."
His solicitors, Ciaran O'Hare and Paul Farrell of McIvor Farrell, insisted certainty was needed on the issue.
They said: "In the absence of government policy we are exposed to political trade winds and uncertainty."
Following submissions the judge, Sir Paul Girvan, reserved his decision on the challenge.