A seven-judge Supreme Court has unanimously refused to order a re-running of the 2012 Children’s Referendum after finding a Dublin woman had failed to prove an unconstitutional government information campaign “materially affected” the Yes outcome.

The court clarified the test which must be met for a challenge to a referendum or election result to succeed, warned of an “inevitable danger of partiality” from government information campaigns which differ from those of Referendum Commissions and stressed the need for “every conceivable care” to be taken to ensure fair running of referendums.

Mr Justice Donal O’Donnell said “unacceptable interference” with the will of the people arose from the Government’s information campaign in this referendum, involving an unlawful spending of €1.1 million from the public money on a one-sided campaign favouring a Yes vote.

If spent lawfully, that money would have just duplicated the efforts of the Referendum Commission established to provide “fair and neutral” information to the people, he said.

Of particular importance in this case was Article 6 of the Constitution, a “powerful republican statement” that the “sole temporal source” of power in this republic is the people themselves.

Mr Justice Frank Clarke agreed with the clarified test for referendum challenges, but stressed when, unlike the Children’s Referendum (passed by 58 to 42 per cent of the 33.49 per cent turnout), the margin in a referendum is very small, “a very different finding” could be reached.

In the case of elections, a candidate may be deprived of victory over established serious misbehaviour in the electoral process even it it was not clear that misbehaviour affected the outcome in the sense of those elected, he said.

In four concurring judgments, the court dismissed Joanna Jordan’s challenge to the constitutionality of laws governing the bringing of petitions disputing the results of referendums, with the effect a certificate making the referendum result final can now be issued.

Ms Jordan, Glenageary Road Upper, Dun Laoghaire, who campaigned for a No vote, previously obtained leave to bring a petition aimed at overturning the Yes result. She relied on the McCrystal ruling the Government spend of €1.1 million public monies on a one-sided information campaign was in clear disregard of the constitutional limits on what the State may do in a referendum.

She also relied on landmark Supreme Court decisions in proceedings by former Green Party MEP Patricia McKenna – which established what are known as the McKenna Principles – that the State is constitutionally prohibited from spending public monies to advocate support for a particular side in a referendum.

The High Court rejected Ms Jordan’s petition on grounds she had failed to prove, as the 1994 Referendum Act requires, that the Government’s information campaign “materially” affected the outcome. It also dismissed her claim the “material” affect standard was impossible to prove and therefore unconstitutional.

All seven Supreme Court judges agreed that what is required in cases where a breach of the McKenna Principles is found, as in this case, is “a harmonious balance” between the competing constitutional principles, obligations and rights.

In order to find a balance between making it “too easy” to overturn a decision of the people, and making a genuine challenge so difficult as to be practically impossible, the court said it had clarified the test for establishing “material affect”.

It clarified that challengers to referendums must establish it is “reasonably possible that the irregularity or interference identified affected the result”.

The object of the test was to identify the point at which it can be said “a reasonable person could be in no doubt about, and no longer trust, the provisional outcome of the election or referendum”, the court said.

Applying that test to this case, the court said relevant factors included the McCrystal decision, the actions of the Minister for Children, the referendum result and the fact the court had ordered a remedy in the McCrystal case.

Taking all those factors into account, the court ruled it had not been established it was “reasonably possible” the actions of the Minister for Children materially affected the outcome of the referendum as a whole.

The Chief Justice, Ms Justice Susan Denham, said there was “ample evidence” to support the High Court finding Ms Jordan called “entirely insufficient” evidence to show the information campaign materially affected the outcome. A reasonable person could not have a doubt about, and would trust, the provisional outcome of the referendum.

Mr Justice O’Donnell said the Constitution does not require that a material effect on the result of a referendum or election must be interpreted as meaning an effect that must necessarily have altered the result, even as a matter of probability.

The test was whether it was reasonably probable the irregularity or interference affected the result and Ms Jordan’s evidence fell decisively short of that standard, he said.

He hoped the judgment would clarify the position and limit referendum challenges to matters with “a real likelihood” of setting aside a result.

This case illustrated the importance of the need for those with the relevant power to strive to ensure future referenda “should be resolved in the ballot box” and not give rise to disputes and differences resulting in court proceedings.

The responsibility for the “unacceptable interference” with the will of the people which the process occasioned in this case could be traced to the decision to spend €1.1 million public monies “in a very short and sensitive period”.

In their judgments, Mr Justice Clarke and Mr Justice John MacMenamin respectively engaged in detailed examinations of issues concerning the use of survey and expert evidence in such challenges.