And Real Madrid - Franco's team - was to be deified. Officially. State-controlled Spanish television continually showed highlights of Real's matches and very little of Barça's, thus generating the notion among the populace that Real were Spain's team. A Franco stooge Barça president managed to 'lose' Alfredo Di Stefano to their arch rivals when they'd already signed him. Di Stefano went on to lead Real to five successive European Cup victories.

The Spanish referees were also got at in a regime of terror. Not only did they favour Real in any encounter with Barça, the 1940s, 50s, 60s and 70s were also littered with bizarre - and obviously biased - refereeing decisions in other matches involving Barça which cost them championships and Cups. The decisions were so appalling that eventually even a puppet Barça president had the temerity to complain to the Spanish College of Referees. He was ignored.

One of the most notorious incidents of Francoista interference occurred early on in the regime. In the second leg of the semi-final of Generalissimo's Cup in 1943 - Barça having won the first leg 3-0 - the Director of State Security came unannounced into the Barça dressing-room in Madrid and scared the living daylights out of them with veiled threats about their long-term personal safety. Barça promptly lost 11-1 to Real.

Real and the Franco-controlled Spanish Football Federation also played fast and loose with the signing of overseas players (then restricted to two per club) until Barça produced documentary evidence that a majority of the South American players with Spanish nationality actually had bogus passports. Of course, Barça had been denied this perk. The practice stopped when Barça threatened to reveal all.

Real's European successes were very useful to Franco. Snubbed by the United States and Western Europe because of his fascist dictatorship, Franco used the team as roving ambassadors to build diplomatic bridges to ease Spain's diplomatic and economic isolation. As one Franco Foreign Minister put it: "Real Madrid is the best embassy we ever had."

After Franco's death in November 1975, Barcelona - still worried about the repressive nature of the regime left behind - covertly organised a demonstration of Catalan nationalism a month later when they were playing Real in the Nou Camp. Seven hundred huge Catalan flags were smuggled into the stadium under the noses of the police. Just before kick-off, the stadium was awash with yellow and red.

It was the first public display of Catalan defiance since the dictator's death. And Barça's winning goal that day was scored in the last minute by Charly Rexach, today the Barça coach. This goes some way to explaining why he said, before these semi-final matches, that beating Real in the semis was more important than winning the European Cup itself. And why the Spanish called it: the Duel of the Century.

The English have a long association with the club going back to its inception in 1899 providing a host of coaches. In modern times Terry Venables and Bobby Robson coached them. Gary Lineker played for them. As did Scottish Steve Archibald and Welsh Mark Hughes. (They would be seen as English by the Catalans).

All of them had never experienced anything like being part of Barça, especially against Real. "It is the only fixture in the world which draws more than 100,000 fans twice a year," Robson said in 1997. "Throw into that equation all the history, the politicking and the media attention, and you're looking at a powder keg."

When Lineker climbed the six steps that lead to the pitch for his first Barça-Real derby the sound overwhelmed him. "This is no derby," he recalled, "this is Catalonia against the rest of Spain, and I'm one more soldier in the Catalan army."

When Venables clinched the Spanish championship in an away game with Barça he was more than overwhelmed. "When we arrived at the airport and got into the bus, there were so many people that a journey that should have taken 25 minutes took seven hours," he remembers. "It was incredible, as if we were the triumphant army that had returned after achieving the impossible.

"It brought home to me that the suffering of the past was something that had stuck these people together, through generations. I felt it had nothing to do with sport at all." Som mes que un club. More than a club.

Forty years ago Barça were the first team ever to knock out the five-times unbeaten champions of Europe, Real. Tuesday's defeat was the first time Real had won in Nou Camp for over 18 years. There is some history between these clubs.

In Steve McManaman's words: "The second leg will be a corker. The fact that we're 2-0 up, doesn't necessarily mean it's all over."

Nor the war.

As the Communist Catalan detective novelist and literary intellectual, Manuel Vazquez Montalban put it: "If Real Madrid didn't exist, someone would have had to invent it."

There is wonderful account of the history of the club in: Barça, a people's passion (Bloomsbury) by Jimmy Burns for those who wish to know more.