The agreement includes a minimum 35% turnout for the outcome of the referendum to be valid. The parties also reached an agreement on topics that would be off-limits to referendum decisions.

These comprise emergency measures in case of natural disasters or defence of the country, in cases of risk to human rights and fundamental freedoms as well as fiscal issues.

The compromise proposal is for the National Assembly to have the right to call a referendum on its own initiative, but would have to call it at the request of 40,000 voters.

A referendum could no longer be initiated by one third of members of the National Assembly or by the National Council, the upper chamber of parliament.

The tentative compromise for the minimum turnout was reached by all parties bar the junior coalition New Slovenia (NSi).

But even without that party, the necessary two-thirds majority has been secured in parliament for the changes to be enacted.

Asked whether the unity augured well for the introduction of the fiscal rule of zero or surplus deficits into the Constitution, Janša said the two constitutional changes were not directly connected.

He also expressed the hope that there would be no direct link with the procedure for the fiscal rule where everyone backed such a constitutional change at first but some withdrew their support later.

Parliamentary Speaker Gregor Virant, who drew up the draft proposal of constitutional changes to referendum provisions, labelled today's compromise good and sensible.

Considering the high level of consensus, he said the best scenario was for the changes to be passed by the summer recess in mid-July or alternatively in September.

By then all the parties would have to endorse the changes at the level of relevant party bodies, Janša said, adding that enacting the changes in July would be a big step forward and a positive message to the public.

Virant suggested that the changes would not affect a potential referendum on the omnibus act on the balancing of public finances for which signature collection is currently under way.

Leader of the opposition Social Democrats (SD) Borut Pahor said that he had suggested changing the referendum provisions after it turned out some MPs opposed introducing the fiscal rule believing it to be a covert attempt at restricting the right to a referendum.

Pahor labelled today's consensus as a big step of the kind not seen for the past 20 years.