Prom 31: Benedetti, BBCSSO, NYOS, Runnicles, ***; Prom 32: Bernstein's 'Mass', Jarvi, *****

Since the first item of Prom 31 was James Macmillan's ‘Fanfare Upon One Note’, it looked - when the orchestra broke into the national anthem - as though this congenitally dour Scot had gone satirical.

But no such luck: after half a verse - it was only minor royalty - the real fanfare struck up. The programme-note described this as ‘a nod’ towards a Purcell fantasia, but it was three minutes (going on ten) of the drabbest and most grimly testosterone-fuelled brass din I’d ever heard: please consign to Room 101. After which Wagner’s prelude to ‘Die Meistersinger’ - a real brass fanfare - came as a relief, with conductor Donald Runnicles and the combined BBC Scottish Symphony Orchestra and National Youth Orchestra of Scotland purveying it with conviction.

This being Scottish night, next up was the youth orchestra plus Nicola Benedetti in Bruch’s ‘Scottish Fantasy’, a rumination on Scottish folk-songs which demands much virtuosity of its solo violinist. Benedetti played with sweetness and accuracy, but most of the time her mousey little sound was scarcely audible. Then came a musical joke - with the shortest and least pretentious programme-note in Proms history - by 84-year-old Thea Musgrave: scored for virtuoso tuba and orchestra, ‘Loch Ness - A Postcard from Scotland’ proved nevertheless musically fascinating.

The next night belonged to Wales, and under the baton of Kristjan Jarvi there came something wonderful: the 41-years-belated Proms premiere of Bernstein’s ‘Mass’, which an army of Welsh orchestras and children’s and students’ choirs (plus a rock and blues band) turned into an earth-shaking event. Conceived out of Sixties anti-war counter-culture, with its libretto co-created by the writer of ‘Godspell’, this (intensely religious) subversion of institutionalised religion still has the power to shock, and with the Danish baritone Morten Frank Larsen as the Celebrant it did so in spades.

For this is a Mass which goes epically wrong, as the Celebrant’s complacency is punctured by the increasingly insistent questioning of his flock: ‘I believe in God/ But does God believe in me?’ Larsen rivetingly enacted the breakdown of his ecclesiastical belief (and his self-belief), while the Street People, Rock Singers, massed choirs, and multiple orchestras delivered the pumping rhythms, bluesy riffs, and choral shouts till the rafters rang. A bold, brilliant, and beautifully-shaped work, and a gilded, glorious performance.