There is a shrug lingering somewhere in Ferran Pedret's shoulders.

The Catalan socialist reckons he has an idea, a big idea, that could save Spain. But he also knows that - for now - Spain doesn't want to hear it.

That's because Pedret is a federalist. And Madrid's Conservative rulers - and even some of the Socialists hoping to replace them - have no interest in a federal solution to Catalonia's yearning for independence. Most Spaniards won't acknowledge that their state, like the UK or the Russian Federation, is pluri-national. The Catalan Socialists, however, do. But it isn't helping them in the polls.

"We seem strange," admitted Pedret in Barcelona last week. "We seem strange from a Catalan nationalist view and we seem strange from a Spanish nationalist view.

"Me, as a Catalan, I can live in a state that is not the nation state of the Catalans. You can think of the Spanish as a nation of nations. But Spanish nationalists don't agree. That is one of our main problems."

Here, in a few lines, Pedret has summed up Spain's Catalan headache. His Partit dels Socialistes de Catalunya or PSC is tanking.

Next Sunday - September 27 or 27S - Catalans go to the polls for parliamentary elections which independence supporters are regarding as a proxy referendum.

A newly forged alliance of pro-independence parties will probably win, aiming to turn Catalonia into a new sovereign state within 18 months.

The PSC will be squeezed by the surge of the independentistas, a new ultra-nationalist force called Ciutadans, and a combined slate of anti-establishment, anti-austerity and green politicians.

Spanish federalism, like the PSC, may be mortally wounded on September 27.

Pedret, already speaking with the frankness politicians usually reserve for concessions of defeat on election nights, is open about the challenge his party faces, even in convincing PSOE, the federated Spanish socialists.

"We don't give up so easily," he says. "We are trying to convince our partners in the rest of Spain and we are having some problems. But we are also finding allies to say that Catalonia is a nation.

"The PSC has always stated that objective fact. We don't agree that every single nation has to reach statehood. We believe in pluri-national states.

"We're working for a federal state for a federal Europe and - let me dream - for a federation of all mankind."

The 36-year-old is from the Catalanista wing of his party; he's a bit like a Scottish Labour home ruler. He believes that each period of Catalan self-rule has come with the help of the Spanish left.

That irks independendistas. "We are exhausted with this idea that the Spanish left in the end will change Spain," said Marc Guerrero, a deputy from Convergència, one of the parties in the new Junts pel Sí or Together for Yes slate. "Well, we have been waiting for a long time. The only federalist party in Spain is the PSC. They are a tiny minority."

As recently as 2006 the Socialists ruled Catalonia, in alliance with another party now in Junts pel Sí, Esquerra Republicana.

The then PSC leader, Pasquall Maragall, was firmly Catalanista. His image, to the fury of some in the PSC, is now being adopted by some independentistas. His brother, Ernest, is now on the nationalist side. Maragall himself, his image and legacy fought over, has Alzheimer's.

The PSC's decline - it may get just 10 or 11 seats in Catalonia's 135-seat parliament next week - mirrors that of Scottish Labour. So does its history.

This party, until 2011, always delivered more seats than any other from Catalonia to the Spanish parliament. The Spanish socialists need those Catalan PSC deputies to win.

Catalan watcher Michael Keating, a professor at Aberdeen and Edinburgh universities, stresses the parallels with Scotland.

He said: "There have always been two wings in the PSC, the Catalanistas, who favoured home rule and a pro-Spain side, the Espanolistas. And there have always been a lot of tensions between these two wings, just as there were over devolution in the Labour Party.

"True, Labour Home rulers seem to have disappeared but they too were always part of the party's Scottish tradition.

"The PSC, like Scottish Labour, has been squeezed, not just by independence supporters and Ciutadans but by the radical left too."

The PSC hasn't always been helped by their comrades in Madrid. Last month Felipe González, the first post-dictatorship socialist prime minister of Spain, published an open letter to Catalans.

This was his Gordon Brown moment, an attempt to mimic the former Labour prime minister's re-invention last year as father of what he saw as an inclusive union. It didn't work. The Catalan independence movement, he wrote, "is more like a German or Italian adventure of the 1930s".

Its result, González added, will be to create a state isolated like that of Albania in the late 20th century.

The euphemisms did not escape Catalan independentistas. "That was disgusting," said Guerrero, citing the González letter. "The Spanish left call us almost Nazis, openly, without any problem."

And here Guerrero hits on another headache for those who wish to retain Spain: the way some people living in Spanish-speaking Spain talk about Catalans, the anti-nationalist passions elsewhere in Iberia that, in turn, fire the flames of nationalism rather than quell them.

Not all Catalans support independence, far from it. The two pro-independence slates look set to get half the vote in next week's elections. But stereotypes of Catalans - sometimes called Polacos or Poles by racists - abound: they are thrifty, they are mean, they don't want to share their wealth, their economic superiority over the rest of Spain.

Indeed, many Spaniards barely seem to have engaged with pro-independence arguments.

A Barcelona cultural organisation, Omnium, recently measured the proportion of independentista voices discussing Catalan questions on the round tables or "tertulias" beloved of Spanish-language TV.

They calculated a figure of four per cent. The equivalent on Catalan-language television was 48 per cent.

This resonates. So do thinly veiled threats. Spain's minister of defence recently said the military would have to "do its duty" in Catalonia.

The response? On September 11, Catalonia's La Diada, its national day, a million and a half, perhaps two million people took to the streets to demand independence. That is up to one in four Catalans.

Among them was Marcel Cano, a 49-year-old philosophy professor. "I have nothing against Spanish people," he said. "It is their government I do not like. But every time it tries to make us afraid, the more of us start to believe we must have our own state."

Catalan nationalists have long had what to their Scottish counterparts appears an unlikely hero: David Cameron, the British prime minister who "let" Scotland have a vote they are being denied.

Now Spanish unionists - as the Catalans hold a proxy indyref campaign - are also learning from the British, from the toolbox of Project Fear.

But can they also learn to adopt Cameron rhetoric, of a Spain, that, like the UK, is a "family of nations"?

Michael Keating, who stresses the divisions within Catalonia on independence, isn't convinced. "There is no will to change the centre," he said. "Outside Catalonia and the Basque country there is a growth in centralist sentiment."

So what of the federalism of Ferran Pedret and the PSC? Can it survive?

Can Spain ever, formally, recognise that Catalonia, with its own language, history and culture, is a nation?

Or would that pose far too dangerous an existential question: if Catalonia is a country, then what is multi-cultural, multi-national Spain?