Are we about to say adios to El Clasico?

In it, Barcelona's central defender is hunched down behind his 20-month-old son, Milan, whose mother is the Colombian pop singer, Shakira. Milan is wearing Barca's away strip, which is modelled on the Senyera, the yellow-and-red-striped colours of the Catalan national flag.

Local police calculated 1.8 million people had congregated for a march to promote Catalan independence, with Pique among them, exhorting his 9.4 million Twitter followers to enjoy a "Happy Catalonia Day", as it was September 11, La Diada, Catalonia's national festival. (Tellingly, Madrid's government delegation in the city put the number of protestors at around 500,000.) The marchers formed a "V" along Barcelona's avenues, Diagonal and Gran Via, to denote "victory" or "vote", which was a nod towards a referendum on Catalan independence then scheduled for November 9.

Little Milan became a socio (member) of FC Barcelona when he was born. Pique's grandfather, Amador Bernabeu, was a vice-president of the club; Pique has said he would like to become the club's president one day. When he was asked during a press conference about his participation in the march, he defended his position. Xavi Hernandez, the club's playmaker, also came out in support of the Catalans' right to vote on independence.

Pique, like Xavi and the other four Catalan players, including Chelsea's Cesc Fabregas, who played in the 2010 World Cup final for Spain, are in an invidious position. They are Catalans yet they play for the Spain national team. Pique said his duality is not a problem: "No one can doubt me: I've played for Spain for 11 years. I feel Catalan and I'm in favour of the referendum, which is a democratic process, but that has nothing to do with the national team."

Meanwhile, the Catalan national team, which is older than the Spain team, plays "international" matches every year and has claimed some notable scalps including that of Argentina in a 4-2 win in 2009. Its federation is not recognised by FIFA, though, unlike the football association of, say, Scotland.

Instead of a competitive national team, Barca has become Catalonia's unarmed army internationally. Its successes are touted as victories for Catalonia. During matches at the Camp Nou, banners written in English for an international TV audience are draped around the stadium: "Catalonia is not Spain". Catalan flags pepper the terraces (alongside Scottish Saltires out of solidarity with its independence movement).

Catalonia's population of 7.5 million is full of migrants, including a huge number who came north from Andalucia in the 1960s hunting for work. Many of these migrants, a million of whom support Real Madrid, think of themselves as a besieged minority, like a mining camp deep in Comanche territory. They resent the fact that their kids are taught to sing the Barca anthem in school and the way Joan Laporta, Barca's most successful president, aligned the club with the Catalan independence cause during his time in power from 2003 to 2010 (before he launched an abortive move into politics).

"It is history," says Laporta. "From the beginning of the twentieth century, Barca has always been considered the club of Catalonia. Why? Because the board of directors in a general assembly supported the Estatut de Catalunya [a statute which defines its self-governing rights] in the 1930s and during my presidency, in 2006, we supported the new Estatut de Catalunya.

"Since [General Franco's death in 1975], Catalan rights are not being promoted and if we don't promote our rights, who is going to? Of course under [Franco's] dictatorship, the repression was more evident. The Catalan language was forbidden. But today we are in the same process. Barca is a representative of Catalan culture, a symbolic church for our country. It is a way to promote our feelings, the best possible tool to promote the image of Catalonia to the world. It's very important because we are giving a cause, a sense to our club, a reason to exist."

Laporta speaks Catalan, as does Pique, as his first language. Catalan is closer to French than it is to Spanish. Madrilenos call Catalans polacos because of the strange, slurping sound of their tongue. There is a clause in Barcelona's contracts that its players must embrace the Catalan language. Barca's captain, Andres Iniesta, for example, grew up in Castile- La Mancha, Don Quixote country in the heart of Spain, but was schooled from 12 years of age at La Masia, Barcelona's youth academy. During radio and television interviews, he fields questions in Catalan but responds in Spanish.

When Pep Guardiola was leading Barca towards two Champions League titles in 2009 and 2011, the then Barca manager spoke in Catalan during press conferences. On Catalonia's national day in 2012, Guardiola, who was on sabbatical in New York, sent a video message in support of separatist protestors marching through Barcelona: "Here's one more vote for independence."

Guardiola is Catalonia's most iconic sports personality. He was given a gold medal by the Catalan parliament, the region's highest honour, in 2011. He embodies "seny", or commonsense, one of the traits Catalans like to define themselves by, the other being "rauxa", or madness. Barca's other totem figure, Johan Cruyff, Catalonia's illustrious adopted son, is the essence of "rauxa" with his prickly, contrarian view of the footballing world.

"Cruyff when he was a player and manager at Barca was always doing revolutionary things because he came, rather like the Catalan chef Ferran Adria, from a working-class background," says the English filmmaker Justin Webster, who lives in Barcelona. "Nobody's taught them to do anything. They start with a blank slate and they invent themselves. That appeals very much to a Catalan idea - they're absorbed with reinventing the nation."

If Catalonia, which has a democratic parliament older than Westminster, succeeds in reinventing its nation, it risks having Barca turfed out of La Liga. A couple of weeks ago, Javier Tebas, the president of the Spanish Football League, said during a sports conference in the Catalan capital that Barca would not be allowed to play in the Spanish league if Catalonia seceded, although there are precedents in European club football such as Monaco in France, as well as Swansea City and Cardiff City in England's Premier League.

"Barcelona wouldn't be allowed to play. There would have to be a change made in the law in the Spanish parliament," said Tebas.

And Tebas knows his law; he is a lawyer by training. He is also right wing by disposition. Tebas, like Real Madrid's former president Lorenzo Sanz, was a youth member of Fuerza Nueva, Spain's fascista version of the BNP, which disbanded in 1982. His hard-line approach reflects the position of Mariano Rajoy, Spain's Prime Minister, who has refused to negotiate with Artur Mas, the political leader of the Catalan separatist push.

Mas, the leader of a coalition government in Catalonia, has capitalised on the recession and voters' insecurity to push for greater concessions from the Spanish government. Chiefly, Catalans want to reduce their contribution to the central government's finances, which is used to prop up less wealthy regions in Spain. According to the OECD, Catalonia generates 19 per cent of the country's gross domestic product, which is higher than the European Union average, while accounting for 16 per cent of Spain's population.

Last week, under pressure from Spain's constitutional court, the parliament in Catalonia decided to cancel its referendum on November 9, which has diverted a potential constitutional crisis. Mas will go going ahead, however, with a watered-down "consultation" on the same day. The informal ballot will not carry as much weight with the world's media.

Polls suggest the blow to Mas's political prestige might drive voters towards his more extremist, junior partner in government, the Esquerra Republicana de Catalunya, who are calling for a unilateral declaration of independence.

One of Esquerra Republicana de Catalunya's members, Josep Sunyol, was Barca's president when Franco's forces killed him during the Spanish Civil War in August 1936. His body has never been found.

Barca's marquee summer signing, Luis Suarez, is likely to make his debut on Saturday against Real at the Bernabeu. A win for Barca would push them seven points clear of their rivals in the league table, and it might fuel Catalan calls to take a bite out of Spain's nation state.

Richard Fitzpatrick is the author of El Clásico: Barcelona v Real Madrid, Football's Greatest Rivalry. It is published by Bloomsbury.