It was not the traditional Wagner production that you might have expected from his great-granddaughter – particularly not at the Bavarian festival of Bayreuth, for more than 100 years the spiritual home of Wagner worship. Bayreuth was, after all, founded by Richard Wagner and is still run by a Wagner, the composer’s 88-year-old grandson, Wolfgang, who has been in sole charge since 1966.

As for Wagner’s penultimate masterpiece, Die Meistersinger, this is an opera set in a happy neverland of 16th-century Nuremberg, which extols the holy virtues of German art. Its hero, Hans Sachs, stands for all that is good and true against Beckmesser, the stodgy conservative. In a plot twist worthy of Pop Idol, Sachs coaches a plucky outsider to triumph over Beckmesser by singing him off the stage in the city’s talent show. The final message, sung first by Sachs and then the whole populace, is “honour your German masters” – a paean, it’s probably worth stressing, to Germany’s cultural, rather than her military, champions.

But 29-year-old Katharina Wagner, daughter and putative heir to Wolfgang, saw it rather differently in her recently unveiled production. As Sachs delivered his final, rousing speech, he was unmasked as a brutal reactionary, setting alight to a gagged conductor and theatre director while the cheery populace saluted. As for those German “masters”, the totems of Teutonic culture were shown in Katharina’s staging as cavorting plastic giants sporting rubber dildos. Whatever triumphed in this scenario it certainly wasn’t the German spirit: Katharina’s final tableau depicted a mass sell-out to ignorance and mob rule.

Has an ideological revolution finally come to Bayreuth? The timing for Katharina’s festival debut – greeted by ferocious booing – is certainly apposite. The members of the Richard Wagner Foundation, the nominal supervisors of the Bayreuth Festival, are again preparing to meet in the autumn to discuss the thorny matter of who will succeed the wily Wolfgang as boss of the festival. As most saw it, this was Wolfgang’s chance to show that his daughter has enough spark to handle the show.

But there are murkier issues behind the Bayreuth curtain than just the battle for succession. In a fascinating new study of the Wagner family – from the composer’s widow, Cosima, right up to the present day – Jonathan Carr has charted in forensic detail the sections of family history that will never have made it into official festival literature, including the true extent of their association with Hitler and the Nazis.

The conclusions are as grimly compelling as they are soberly delivered. Unlike the most blinkered detractors of both Wagner and the Wagners, he doesn’t rush to find links that don’t exist between the music and the political ideology. Indeed, one of Carr’s most intriguing findings is how the number of Wagner performances declined during the Third Reich, and that many of the party faithful were turned off by five-hour Wagner marathons, preferring light operetta or jazz.

But what he does reveal, in the most gripping section of the book, is the depth of the assocation between the Bayreuth management of the 1930s – headed by Wolfgang’s mother, British-born Winifred Williams – and Hitler. Fascinated as much by the cosy family set-up of Bayreuth as much as by his musical hero, Hitler gave them his personal protection and backing.

In 1934, he had Joseph Goebbels buy up enough tickets to make up a third of the festival’s budget; in 1939, the Führer’s personal office subsidised Bayreuth to the tune of half a million marks.

As for Wolfgang and his siblings, provided that they professed their loyalty they would be personally rewarded. As Carr recounts, Wolfgang got a shiny Mercedes from the Führer when he passed his driving test, and, when invalided out of the Second World War in 1939, received a personal visit while recuperating.

As the war went on, Bayreuth remained an unreal oasis, attended by tens of thousands of workers and soldiers bussed in by the Nazis. The final wartime performances, in 1944, featured SS members drafted into the depleted chorus. What was the opera? Naturally, Die Meistersinger.

But perhaps worse than Carr’s careful detailing of all the kickbacks the Wagners received under the Third Reich was the family’s lack of readiness to own up to it afterwards. Only one Wagner grandchild, Friedelind, fled Germany during the Third Reich and opposed Hitler. But when she returned to the festival, in 1952 (the brothers Wolfgang and Wieland had opened shop again in 1951, requesting visitors to “desist from discussion or debate of a political nature”), she was comprehensively rebuffed as an oddball rebel. Worse, as late as the 1960s, the ghastly Winifred, who had always maintained that her regard for Hitler was purely “personal”, was entertaining far-right German politicians at Bayreuth as well as Oswald Mosley. So much for “no political discussions”.

It is this inheritance, Carr implies, that has poisoned the Bayreuth legacy, and continues to warp its artistic aspirations. His book finishes on the eve of Katharina’s festival debut: seen against his research, her iconoclastic production (and her ostentatious courting of the audience’s boos) might just be a belated admission that the festival’s cultural certainties could do with some serious interrogation. Whatever the shortcomings of a staging that most critics felt was muddled in the extreme, it is a laudable ambition.

The question is how far she intends to go now. “Bayreuth has gained a certain mythological status,” she admitted recently. “If you scratch this status, you have to be aware of the consequences.”

Should she take over the family business, she’ll certainly need more than rubber dildos to wipe the slate clean.

Jonathan Carr’s The Wagner Clan is published by Faber on September 6. For information on the Bayreuth Festival, go to www.bayreuther-festspiele.de

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