WHEN Simon Callow played Mozart in the National Theatre's original 1979 production of Peter Shaffer's play, Amadeus, part of his preparation for the role was to make it look as if he knew what he was doing. As an actor dedicated to his craft, such intensive research wasn't unusual for Callow. Amadeus, however, introduced a new challenge for him.

“I had to go to great lengths to impersonate a man playing the piano,” says the actor and writer still most familiar to many from his appearance in Richard Curtis' film, Four Weddings and a Funeral. “I thought it was important to try and get the movement right when I sat at the piano. Paul Scofield, who was playing Salieri, had no interest in any of that, but I really sweated over it.”

Thirty-seven years on, Callow appears onstage tonight alongside music of a very different kind as part of the Aberdeen-based Sound festival of new music. He will be the sole actor in De Tribun (The Tribune or the Mother of all Speeches), a piece by Mauricio Kagel. The Argentinian-born composer lived for much of his life in Germany, where he experimented with fusing musical and theatrical elements. In De Tribun, which is scored "for political orator, march music and loud-speaker", Callow plays a politician rehearsing his speech, stopping and starting pre-recorded applause as he hones his performance.

Kagel composed De Tribun in 1978 when he was living in Cologne in a still divided Germany where a Soviet-backed regime was just a wall away. With his home country ruled by a military dictatorship alongside other South American countries including Chile, Peru, Paraguay and Brazil, Kagel's composition was an absurdist satire on totalitarianism which, in the current political climate, seems oddly familiar.

“It's very chilling indeed,” says Callow as he prepares for the performance. “The character I play is a rabble rouser. He's someone who appeals to the lowest common denominator. He's basically every dictator that's ever appeared, and is very relevant to some of the things that are going on in the world just now.”

Beyond the themes of De Tribun, it was the musicality of the piece that appealed to Callow.

“I was very keen to do it,” he says, “because I love working with musicians. I'm not a musician, and I'm not a great singer either, although I've just sung an aria by Puccini for Stephen Frears. What I particularly like is working with musicians on new music, and although De Tribun isn't new, it's complex and it's difficult and it feels new.

“The music and the text don't overlap each other. It's really a series of marches, and I say this hectoring text, which is underpinned by the music as it gradually becomes clear that the orator wants complete power. It's very raw and incredibly tough. It's really quite something.”

Callow's singular acting style, which can see him occupy the stage with a larger than life presence that can capture a character's full sense of ridiculousness, is perfect for De Tribun's would-be tyrant. Unlike the majority of his roles, however, he didn't have much to go in in terms of research.

“I'm not even sure there's a commercial recording of it,” he says, “although they sent me a version that was in Dutch.”

Callow's performance of De Tribun forms part of Freedom o(r) speech, a triple bill of work co-produced by three major European ensembles – Red Note from Scotland, I Solisti del Vento from Belgium and Song Circus from Norway. As well as De Tribun, the programme features Dutch composer Louis Andriessen's piece, De Staat (The Republic) and the world premiere of The F Scale, a newly commissioned work by Sound's first composer in residence, John De Simone.

Kagel died in 2008, but his pioneering work as a a composer exploring form has left its mark.

“He was an extraordinarily influential figure,” says Callow, “and was one of a generation of artists – Pierre Boulez was another one – who were incredibly important in terms of what they did with music.”

The day after he appears at Sound, Callow will give a morning performance of his solo version of Charles Dickens' A Christmas Carol at the University of Aberdeen. Callow is looking forward to returning to the city.

“I'm so fond of Aberdeen,” he says. “I first encountered the place in 1974 when I was touring with the Young Lyceum company in Edinburgh with a musical called The Fantastics. It was the first time I got to know Scotland properly, and then I visited it again when I directed Die Fledermaus for Scottish Opera, which we toured, and we brought my production of My Fair Lady there as well. But Aberdeen is such a fantastic, noble city built of all this wonderful grey granite. “

Callow's take on A Christmas Carol is a labour of love that continues a love affair with Dickens' work that has seen him perform several adaptations of his novels, as well as lesser known works. The latter includes his double bill of Dr Marigold and Mr Chops, which he brought to the Edinburgh Festival Fringe and later toured.

“Doing a one-man version of A Christmas Carol is a really wonderful way of doing it,” Callow says. “Not only can I move quickly between scenes in what is a phantasmagoria of a story, but most importantly, it means I can keep Dickens' voice.

“One of the interesting things about A Christmas Carol is that it makes everyone feel warm, even though it's actually a terrifying story. Who would want to be dragged through their entire past life and forced to confront all your wrong-doings in the way that Scrooge is?"

Callow is currently trying to make a film of the seasonal favourite which looks set to take a very different approach to Christmas Carol: The Movie, the partly animated feature film, in which Callow led an all-star cast as he provided the voice of both Dickens and Scrooge.

“We're going to do it in quite an experimental way,” he says, “which with only one performer I think is the only way to do it. But I will never ever tire of Dickens. He's the writer who means the most to me. His work is inexhaustible.”

Beyond De Tribun, music looks set to remain a fixture of Callow's working life. In a forthcoming episode of Midsomer Murders, he appears as a viola player. Interestingly, when Callow previously appeared in the programme, he was again cast as a musician, then a violinist.

“That was very strange,” he says. “They had a professional violinist sitting beneath me, and they kept cutting away to him."

Callow has also written a biography of Wagner, which is scheduled for publication this coming January.

“I'm passionate about music,” he says, “even though I was probably the only child in the world whose mother refused to send me to piano lessons.”

Despite, or possibly because of this, Callow's interest in music has seen him host the 2004 Christmas show by London Gay Men's Chorus at the Barbican, and in 2007 he became a patron of the London Oratory School Schola, the boys choir at the Catholic school he attended as a child. Composer James MacMillan is also a patron of the choir.

While it is unlikely that De Tribun will ever be performed at the London Oratory, the themes of Kagel's composition chime beyond pure music to sound a warning bell for us all in terms of who we mandate to hold offices of power.

“I think we are all dealing every day of our lives with a world that is becoming increasingly unpalatable,” says Callow. “But art can make things more meaningful, and with De Tribun I think Kagel was forewarning us about what can happen, and how through art and through his work we can try and make sense of our times.”

Simon Callow performs De Tribun (The Tribune) as a part of Freedom o(r) Speech at Sound festival at ACT Aberdeen tonight at 8pm. Sound runs until November 6.

www.sound-scotland.co.uk