Classical review: Imogen Cooper, Ivan Fischer, Budapest Festival Orchestra, Royal Festival Hall, London

The cadenza in a classical concerto is a curious thing. Originally devised as a way of letting the soloist show off, it became a commentary on the work it adorned, as well as a holiday from it: the soloist could take you on a switchback journey before bringing you safely home. These days, with so many other opportunities for display, its bravura function has faded, so soloists often use it instead as a slot to puff their own wares – as Kennedy does when he injects jazz and Gypsy music into his Brahms.

The cadenzas which Beethoven wrote for his piano concertos are in some cases almost off-the-wall, most notably the alternative one he added as a late afterthought to his first concerto. When Lang Lang played it at the Royal Albert Hall last year, it didn’t sound like Beethoven at all. But as Imogen Cooper delivered it with Ivan Fischer and the Budapest Festival Orchestra, you sensed Beethoven in every bar as it wove in motifs from the first movement and turned them upside down and inside out.

And if Cooper rounded it off with a smile, that fitted too, because her interpretation of the work as a whole was as spirited an account as I have ever heard. While the slow movement had a singing warmth, the opening Allegro became an exemplary display of pellucid passage-work and subtly-shaded perspectives; the concluding Rondo – in which Beethoven plays tricks with the listener’s expectations – was mercurial from start to finish.

Ivan Fischer co-founded this orchestra on a wing and a prayer in the dark days of late Communism, and as the rest of the programme attested, they are now one of the brightest ensembles in the game. Erno Dohnanyi’s Symphonic Minutes allowed them to demonstrate their remarkable ability to create a quick succession of contrasting atmospheres; Dohnanyi’s friend Bela Bartok’s Concerto for Orchestra gave them licence to flaunt their virtuosity and musical wit. This they did in spades, with each player taking a turn in the spotlight.

Like any healthy democracy, this event encompassed its own competing ideologies. Shell was the sponsor, and a group of protesters stalked the foyers with a banner proclaiming "not in our name". Long may Shell continue its invaluable support for such music-making, and long may the environmentalists continue to hold it to moral account.

On Saturday 27 April the Budapest Festival Orchestra will perform at the Marlowe Theatre in Canterbury.