Confined to her room with a cup of tea and treated by Carson as though she was a visiting tradesperson during her visit toDownton Abbey? The real Dame Nellie Melba wouldn’t have tolerated such treatment for a nanosecond. In 1922, she had enjoyed 30 years of being received as a social equal by crowned heads and aristocrats throughout Europe, and she would only have sung at a private party as a personal favour to her host. Melba was nobody’s hireling: she called all the shots, and the Granthams and their staff would have quaked at her approach.

Kiri Te Kanawa in Downton Abbey's drawing room

Impersonating this gorgon, Dame Kiri Te Kanawa at 69 looked much younger and more glamorous than the real Melba (who in 1922 would have been eight years younger).

But she sounded rather worse - recordings of the Australian soprano dating from that era demonstrate singing far more secure and shapely than Dame Kiri’s. Sharp unsteady intonation, heavy vibrato and tastelessly swooping portamento vitiated what fragments we heard of her performance of two arias by Puccini and a song by Dvorak: the dastardly Green’s reference to the noise of ‘a cat on a bonfire’ was unkind, but Mrs Patmore’s expression of heavenly rapture was scarcely convincing, and no wonder that poor Anna Bates whisperingly complained of a headache.

Dame Kiri delivered a few lines of dialogue in stiffly parroted and nervous fashion which reminded me that even in her glorious vocal prime she had never been much of an actress, while her flatly modern mid-Atlantic accent was nothing like Melba’s cultivated diction (of which evidence survives on a recording of her farewell to Covent Garden in 1926). I greatly admire the shrewd casting of Downton Abbey, but this was not one of its happier inspirations.

Two footnotes: at dinner, Melba-Te Kanawa admitted to a study of claret and a fondness for Haut Brion: the real Melba was rumoured to be not so much a sophisticated oenophile as something of an old soak, but dedicated professional that she was, it is highly unlikely that she would have touched throat-desiccating alcohol just before singing. And I was unconvinced by Isobel Crawley’s expressed preference for the music of Bartok, which had barely registered in the Britain of 1922 - a douceur for Debussy might have rung a little truer. In other words, Downton Abbey’s cultural pretensions had tripped up once again, leaving the whole episode deliciously ludicrous and emptily improbable.