BBC Proms: Lazić, Budapest Festival Orchestra, Fischer/ Audience Choice Prom

"Don't expect polish," announced Ivan Fischer apologetically. "Things vill go rrrong. We may start pieces again." The tuba had been turned into a tombola. The percussionists were playing their buttocks. Someone else was blowing a Hungarian didgeridoo. A certain amount of madness was expected from the second Prom, an experimental Audience Choice concert. But the Mahler One of the first Prom? Who knew that that would be equally if not even more outrageous.

As Edward Seckerson once wrote on theartsdesk, Mahler is about extremes: extremes of dynamic, tempo and texture. And death-defying extremes we got. There was a Cagean opening hush, a ritardando into the D major explosion that felt like we had all been led into a lake of toffee and almost a school rugby bus feel to the indecently raucous and drunken Scherzo.

The Finale? Literally jaw-dropping. The whole orchestra belted through the final bars as if they had wolfed down a bag of cocaine, chief drug dealer, Ivan Fischer, manically waving section after section to leap to their feet for the last notes. Thank God the piece ends where it does. Such was the exponential accretion of energy, the orchestra was almost left nowhere to go except perhaps up through the roof, Busby Berkeley style.

The whole thing almost totally defied analysis. Fischer had torn to shreds the polite, urtext-bound rule book that still dominates concerts. And he had every right to. Not just because everything he did worked. But also because every detail had its grounding in things Mahler or his disciples had themselves done (such as standing horns). Besides, having been premiered in Budapest in 1889, the work does in some small part belong to these musicians.

The first half was no less breathtaking. Following a sharply defined, brightly coloured opening Mephisto Waltz and a sweet and shapely performance of Mahler's Blumine, the orchestra were joined by Croatian pianist Dejan Lazić for Liszt's monstrous, virtually atonal Totentanz. Lazić and Fischer, two of the livest wires in the business, romped through the work, making a mockery of the technical difficulties they faced. Lazić's staccato keepy-uppy with the near-dodecaphonic arpeggios was finger-defying. There were octave runs and four-octave leaps, all of Olympic standard. Yugoslav-Hungarian hybrids like me don't often get the chance to feel a swelling of nationalistic pride. But one really could here.

Hungarian tafelmusik danced us to the Budapest coffee house

The musicality, the pride, the mayhem: it all continued into the late-night Prom. When English ensembles deliver new-fangled participatory events it's almost always head-in-jumper stuff as they drag their feet through various politically correct and patronising outreach hoops in order to guarantee another year's state funding. Last night couldn't have been further from this teeth-clenching fare.

First, authentic Transylvanian folk music serenaded us to our seats, whereupon the raffle on what the orchestra would play (unrehearsed) began. Three people were randomly (this is where the tuba tombola [pictured right] came in) selected to choose one work each from the 285 on offer. Then the vote - which quickly shifted from a show of hands to a show of brute vocal power. "Brahms Hungarian Dance No 1!", one shouted. "Boring!" we shouted. "Meistersinger Overture!" another hollered. Nah, we collectively thought. "Kodály's Dances of Galánta?" Now we were talking!

A lot of my time at the Proms is spent under-the-breath cursing the noisome tics of the Prommers, dearly wishing that one day I'll pluck up the courage to shout, "Critic to Arena: I Hate You ALL". But last night, I wanted to hug them. The way they overwhelmed the Classic FM tendencies of the audience and steered the night towards the adventurous was terrific. Cruelly, I revelled in the stony faces that descended on the suburban couples in the stalls as yet another chart-topper was rejected.

Josef Strauss's Music of the Spheres Waltz swept aside Mahler's Adagietto. Ruslan and Ludmilla Overture crushed Boléro (for which protest returned - of the right sort). We got rip-roaring Roumanian Folk Dances from Bartók, Stravinsky's Tango and a manic March from Berlioz's Damnation of Faust. All glorious stuff, stylishly done. But the real treats came in the gaps. While the librarian hunted down the scores, Hungarian tafelmusik, folk cello - the gardon - the didgeridoo and resin-encrusted fiddles danced us to the Budapest coffee house. What a triumph of innovation. Bravo, Roger Wright.

After the antics of Thursday, I was fully expecting today to report that everything was back to normal at the Royal Albert Hall. But it wasn't at all. Two more extraordinary days at the Proms can't have ever been seen.

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• theartsdesk's pick of the Proms
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