The more you read about music, the more you notice the word “authenticity” cropping up annoyingly frequently. The great raging musical arguments of the late 20th century still burn; performers, listeners, even composers find themselves having to take up quasi-moralistic stances on gut strings, vibrato, and whether trills should begin on the upper or lower note. The plurality of performance styles that has emerged is a wonderful luxury, but I can’t help feeling sorry for performers like Angela Hewitt, who must have been plagued with criticism throughout her illustrious career for daring to play Bach on a piano. She’s probably used to it by now, and has a handy pre-emptive trick or two up her sleeve. For example, for her The Art of Fugue concert in St George’s – and in venues worldwide – her programme seemed designed to silence sceptics: and her playing, her critics.

The recital began with three works not originally written for single keyboard instruments, transcribed for piano by Wilhelm Kempff, which negated the whole authenticity argument by embracing instrumental “inauthenticity”. Thus we had works for organ, chamber ensemble, and larger ensemble all at the tips of Hewitt’s fingers; a combination that worked so well because each manifested not only varying timbral qualities, but contrasting examples of Bach’s expressive genius, and Hewitt’s exemplary pianism. Nun komm, der Heiden Heiland was perfect in its poise and understatement, the pianist’s voice-leading gently guiding the listener through the intricate textures of Bach’s organ writing. The Siciliano from the Flute Sonata in E flat major was all sweetness without the slightest saccharinity, and the piano sang as Hewitt caressed its keys lovingly. This was not the case in the Sinfonia in D from Wir danken dir, Gott, wir danken dir, where the ebullient triumph of the instrumental writing required much gusto and technical wizardry. Although the embodiment of numerous instruments provoked the occasional smear in pianistic precision, it was glorious all the same.

There is nothing at all Bachian about Beethoven’s Sonata in A, Op. 101, and its inclusion in the concert provided us with some concrete stylistic contrast. Hewitt wasn’t quite as spotless in this work, although the serene simplicity of the short first movement, with its unaffected chordal style, was gorgeous. The assertive second movement has a tendency to romp, and romping is not something that strikes me as something Angela Hewitt is much inclined to do. As such, the recurring March always felt a little uncomfortable to me – although the trio was delightful – and it was with relief that the extraordinary slow, pensive, unresolved opening to the third movement unfurled. This lack of resolution continues in the ensuing Allegro, in which Beethoven never allows the listener to settle by denying the bass to act (as it usually would) as harmonic stabiliser. A fantastic fugue bore well for the second half, but the piece – a funny creation, serious and weighty yet rascalous and teasing – was summed up perfectly by the hint of a 7th (accidentally) appearing in the final A major chordal outburst.

The Art of Fugue is a compositional tour de force, an imposing testimony to the immensity of Bach’s technical genius. As such, it is rarely performed, particularly not on the piano (Bach wrote each of the four parts in open score, and so it would appear more intended for performance by an ensemble – if it was intended for performance at all). The work’s colossal complexity prompted a charming introduction from the pianist, who took us on a witty and entirely helpful whistle-stop tour of the first ten Contrapuncti. This was excellent: we weren’t left floundering in the sea of contrapuntal mastery, but given musical lifebelts, strategically placed to ensure we could float in, and not sink under the weight of, Bach’s fugal intricacies. Really, though, the performance was sufficient. Everyone unerringly fixated the music: and what arrestingly beautiful music it is! Hewitt teased out the idiosyncrasies of each exquisite Contrapunctus without caricaturing them: the playfulness of the imitative “cuckoo” in the fourth; the exaggerated stateliness of the double dots and trills of the sixth; the rapid virtuosity of the ninth; and so on. These “technical exercises” exuded emotion, expressivity and a certain sense of divine spirituality; it was a totally engaging, all-encompassing performance that challenged Hewitt physically and mentally as she wove her way through the endlessly intertwining lines.

But she relished the challenge; only after the last chord had reverberated round St George’s did she show her exhaustion – but the audience launched into rapturous applause, calling her back to the stage again and again. For we realised that this was a true authentic performance, in that word’s boldest, most spiritual sense.