Spain will be the first of the European Union's 25 nations to hold the referendum to accept a new constitution on Sunday - a document designed to simplfy the EU's decision-making process.
The vote, which asks the basic question "Do you approve the treaty instituting a constituition for Europe?", is widely expected to be a yes vote for Europe, with the Spanish government of Jose Rodriguiz Zapatero strongly endorsing it.
But according to Charles Powell, deputy director of the Elcano Royal Institute in Madrid, the lack of higher turnout will reflect badly on the EU and Spain's pro-Europe government.
"People in Spain take Europe for granted. They know that Spain has done well out of Europe", he told Aljazeera.net.
"Do you approve the treaty instituting a constituition for Europe?"
Spain's EU referendum question
The institute, which examines Spanish affairs in a national and international context, believes that Spaniard's attitudes to Europe are a combination of mild enthusiasm and plain ignorance.
"Spain is generally passive because Europe is uncontroversial and there has never been a deep debate about it," he.
Powell said voter turnout could be as low as 40%, adding that this would be embarrasing to pro-Europeans to say the least because last June's Europe-wide local elections had a Spanish voter participation of 45%.
The constitutional vote is even more important, he said, but because Spain is likely to vote "yes", it is considered a forgone conclusion.
A lower turnout will be admission that knowledge and enthusiasm for Europe is something that does not stir Spaniards' passions.
They have been grateful for the two main benefits of EU membership: political stability and billions of pounds of structural funds, which have allowed Spain to modernise its roads for instance.
Socialist Prime Minister Zapatero has been striking an increasingly urgent note as he tries to drum up interest by reminding Spaniards - with expensive advertising campaigns - that they have benefited to the tune of £60bn since joining the EU in 1986.
Spanish people have been bombarded with leaflets as they board trains, queue at supermarkets and wait at doctors' surgeries.
The campaign's slogan, "Los primeros con Europa" (First with Europe), appears on lottery tickets and even football legends Emilio Butragueno and Johan Cruyff have appeared in television adverts, asking people to vote.
Prime Minister Zapatero has
urged people to vote
Yet it's not so much as Euro scepticism as Euro apathy that has caught on in Spain, where the fruits of EU largesse have been on display everywhere.
The "no" campaign which is largely centred in the Catalan region, has not been able to stoke a nationwide debate as to why a "yes" vote would be terrible for Spaniards.
All the arguments used against Europe have not really caught fire, the Elcano Royal Institute's Powell said.
"Conservative's arguments for voting 'no' centre on a suspicion of the European project, the lack of acknowledging its Christian roots, the loss of national soverignty through voting power.
"The leftist argument has been that the way political union is taking place will actually lead to the destruction of the European social model which has guranteed social welfare," Powell said.
"And the Catalan argument has been that by joining Europe Spaniards have been losing their cultural and soverign identity".
Worries for EU
But none of these arguments have had the intended effect, Powell said.
A less than resounding win for the Yes campaign will worry Europe ...
[and] may influence wider apathy. Why bother to vote when no one else does?
Elcano Royal Institute
The impact of a lower turnout will not affect Spain as much as the EU itself. The referendum for the Spanish public is merely consultative, with the parliament actually ratifying the vote. For the EU, the consequences will be political.
"A less than resounding win for the Yes campaign across Europe in Spain today, will worry the governments of France, Portugal and Germany - all of whom are enthusiatic, but their populations less so.
"The close geographical proximity to Spain may influence wider apathy. Why bother to vote when no one else does?"