Prom 55: BBC So / Swensen / Kavakos, Royal Albert Hall, London

All might have been well had it not been for the world premiere of a BBC commission, Strip , which doubtless took the lion's share of rehearsal time. This was the British composer Morgan Hayes's first Prom appearance and first orchestral piece, and he chose to write for a massive orchestra, including cimbalom, harmonium and countless percussion instruments.

In one movement, Strip exudes exotic colours. It begins with woodblocks, log drum, bongo, cowbells and claves, and the rattling, tinkling, banging and scraping runs almost continuously throughout. A lot goes on. Layer upon layer of different lines forge forward with no indication that they relate in any way; colour and volume assume greater importance than harmonic logic in a piece that rarely ebbs. Orchestra and conductor seemed to negotiate the piece well.

Then came Berg's Violin Concerto. In the capable hands of the violinist Leonidas Kavakos and Swensen (once a violinist), all should have been well. Kavakos caught with great tenderness the melancholy of a score written as a requiem for the daughter of Alma Mahler and Walter Gropius. But halfway, a string on Kavakos's beautiful instrument snapped. I've never witnessed a more seamless takeover: Kavakos, with the leader's fiddle, continued to play so smoothly that even the conductor seemed unaware of the drama, and a new sensitivity informed Kavakos's playing.

Beethoven's Seventh started well, the opening chords of the slow introduction full and purposeful, but as it swung into the vivace, exactness of rhythm became a casualty. Swensen took no breath between movements, diving into the funeral march before any Prommer even thought of applauding. If the Scherzo fizzed, the final movement hurtled, but again sacrificing rhythmic precision.