In the Rodgers and Hart musical On Your Toes, a Broadway hoofer is forced to work at a community college, teaching classical music like some kind of square. He picks out a melody on the piano: ‘Whom was this written by?’ ‘By Caesar Frank!’ chorus the students. ‘Pronounce it Fronk,’ he corrects them; and the audience, presumably, laughed in recognition. This was 1936, and César Franck’s Symphony in D minor was a hugely popular concert hall warhorse. Now: not so much. According to the stats in the programme book for this BBC Prom, it was performed 36 times in 50 years at the Proms, before falling off a cliff in 1959. This performance by the BBC Symphony Orchestra under Fabien Gabel was only its seventh Proms outing in as many decades.

So come on then, you who rail against the unchanging canon of western classical music: explain that. It can’t have been the patriarchy this time. Personally, I’m grateful for any opportunity to hear the Symphony played live. Decades ago in the Merseyside Youth Orchestra, I played it 12 times in 14 days, and any music that can stand up to that kind of punishment clearly possesses something enduring. The handful of us who still get Franck’s Symphony really, really get it: it’s become a cult piece, and Gabel, who has guest-conducted several UK orchestras over the past few seasons, appears to be a fellow-devotee. More significantly, orchestral musicians speak highly of him: never an absolute guarantee of musical quality but a fairly reliable indicator that a conductor is – at the very least – worth investigating.

Gabel opened with another Gallic rarity – Lalo’s foamy overture to Le roi d’Ys – and Brahms’s Violin Concerto, preened and manicured into near-stasis by the soloist Daniel Lozakovich. Lozakovich makes a handsome sound, but didn’t seem particularly interested in sharing it with the audience. Throughout, Gabel moved with efficiency and finesse, and the BBC Symphony Orchestra sounded as bright as coloured glass. And then it was César time, and Gabel quickly, elegantly slid the rug out from beneath my feet. Franck’s Symphony has an atmosphere like no other: a fervid, overcast emotional landscape in which Wagnerian mists swirl around red-brick Gothic pinnacles, and the timeworn tools of the Catholic organist-composer – tolling ground-basses, muscular gear shifts, floating veils of harmonic incense – are re-engineered with girders. Two cornets play alongside the trumpets, oxidising the brass sound, then turning fabulously trashy in the finale, where Franck suddenly throws off his Lisztian surplice and goes full ta-ra-ra boom-de-ay.

Gabel’s approach was unexpected – lyrical, reflective and dappled with moments of delicate, glinting sunlight (only Franck, among his Franco-Belgian contemporaries, would deploy a harp in order to channel it below the music’s surface like the waters of a subterranean canal). The central intermezzo became a sinister passacaglia, with plangent cor anglais and hovering strings falling in behind one another in a slow but ineluctable procession, and the end of the symphony was like a slow-motion sunburst. I’d been holding out for a performance that would overwhelm the unbelievers with blazing balls-to-the-wall affirmation. Gabel wasn’t in that game. This was an interpretation that could only have come from a conductor who knows this Symphony intimately and loves it deeply, and I felt ashamed of my adolescent instincts as I left the hall.

Verdi’s Falstaff takes Shakespeare’s The Merry Wives of Windsor and trims and plumps it into a musico-dramatic masterpiece. Vaughan Williams’s Sir John in Love undoes all those changes and ends up with third-rate Shakespeare set to second-string VW. It’s inventive and polished; the deftness of the musical scene-setting reveals the instinct of the future film composer, without ever getting sufficiently deep below the skin of the (far too numerous) characters to justify its existence as an opera. Vaughan Williams prided himself on using Shakespeare’s actual words (he was dismissive of Verdi and Boito’s ‘medicated Shakespeare’). ‘I’ll no pulletsperm in my brewage!’ bellows Falstaff, and the surtitles seemed to jam. ‘Pulletsperm,’ muttered the chap sitting behind me. Ladies and gentlemen, the greatest poet in the English language.

Sir John in Love certainly provides vivid and singable roles for a large cast and Harry Fehr’s joyous 1950s-set production for British Youth Opera filled them all with talent to spare. Was Johannes Moore too much of a smooth-cheeked charmer to pass as the Fat Knight? No matter: that huge, shining baritone could charm the pants off the entire population of Windsor. Alexandria Moone sang with seductive elegance as Alice Ford, Grace Marie Wyatt was a sunny and sweet-sounding Anne Page, and the Southbank Sinfonia under Marit Strindlund brough shimmering wonder to the brief, moonstruck moments when Vaughan Williams rests from re-arranging his toybox of characters and opens a portal into a deeper, older England. In other words, when he meets Shakespeare on his own terms.