It was fitting that King Juan Carlos should have been among the first people to vote in Sunday’s Spanish referendum on the EU constitution, even if Queen Sofia had to remind him to show his identity card at the polling booth.

Spaniards feel they owe a great debt to their monarch for paving the way to EU membership when he donned his military uniform to denounce the 1981 attempted coup, which threatened to take the country back to the dark days of Franco.

If Spaniards feel affection for the king, they appear largely indifferent to the EU even though it is widely credited with helping to underpin democracy in a country which was still a dictatorship 30 years ago.

As expected, the Yes side triumphed in Sunday’s referendum with about 79 percent of the vote, according to an early exit poll by state television and radio. But the same poll, of 28,000 people, estimated voter turnout at 41.5 percent, meaning that less than half the population bothered to vote in a country which has been showered with 60 billion pounds of EU cash since it joined in 1986.

European leaders were quick to put a positive gloss on the result, as they declared that the better than expected turn-out would boost the ‘Yes’ camp in the nine other countries holding referendums on the constitutions.

Behind the smiles, however, they will be disappointed that voters in one of the most pro-European countries seemed so unmoved by the constitution. As the great and the good of Europe fly into Brussels for today’s summit with George Bush, they will be beset by fears.

A bumpy ride ahead is now guaranteed. If less than half the population can be bothered to vote in a country whose economy has been transformed over the past 20 years there must be severe worries about a new member such as Poland, where the poll will be invalid unless 50 percent of voters turn out.

Even if the constitution is passed by the end of the 18-month referendum season, there will be questions about the entire project.

The constitution was meant to bring the EU closer to its 450 million citizens. Valéry Giscard d’Estaing, the former French president who oversaw the drafting of the constitution, even claimed that its architects would be remembered with statues of them on horseback.

Such hubris is returning to haunt Giscard d’Estaing, though he appears to be supremely unmoved as he sets about living out his last days as an aristocrat in his newly acquired chateau.

Gisela Stuart, the Labour MP for Birmingham Edgbaston who helped draft the constitution, joked last night that there would now definitely be no statue of her astride a horse.

“This does show that the European project is failing to enthuse a new generation,” Ms. Stuart said. “Just one in ten people in Spain said they understood the constitution.”

The bumpy ride ahead shows that that the whole constitution was badly conceived, she said.

“There really are only two sorts of constitutions — one that is a nation’s birth certificate, like the US Constitution, and a second, (like the 1978 Spanish Constitution), which marks a regime change. Neither of those applies to the EU constitution, which means it reflects an ambition that could not be fulfilled.”

Matthew McGregror, of the euroskeptic Center for Social Europe, believes the constitution is now in trouble. “The Spanish government spent a fortune on flash advertising, so the turnout is a knock. It will leave the ‘Yes’ camps in other countries asking how they enthuse people.

“How do they motivate people to vote for something they don’t understand? If they struggle in pro-European Spain, how will they get people out to vote in the Netherlands, Poland and Britain.”

But pro-Europeans were breathing a sigh of relief last night. One European diplomatic source said: “In the absence of an effective campaign in Spain this is a good result. There are more posters in Madrid backing the city’s bid for the 2012 Olympics than there were ‘Yes’ posters.”

Meanwhile Charles Grant, director of the Center for European Reform, believes it is wrong to read anything into the Spanish result.

“This referendum was a nonevent. The whole point about referendums is to settle an important issue where there are fundamentally different opinions. In Spain only nutters are against the constitution. If you have a referendum in such circumstances then the turnout will be low.”

Referendums will really matter, Grant added, in seven of the nine countries holding polls where there are real debates.

The seven are France, Britain, Denmark, the Republic of Ireland, the Netherlands, the Czech Republic and Poland.

“There are real arguments in those countries, so their campaigns will be interesting,” he added.