Martin Graham styled them “the impossible-ists” — the doomy folk who claimed that Richard Wagner’s Ring cycle could never be satisfactorily presented in the little theatre fashioned from a barn beside his and wife Lizzie’s Gloucestershire home. Well — stupendously, emphatically, gloriously — Mr Graham proved them wrong. In four sell-out performances spread over eight days Longborough Festival Opera delivered a magnificent account of Götterdämmerung, the last and longest of the tetralogy, completing a musical mission begun in 2007. The scene is set for three complete cycles to be given next year (between June 16 and July 12) to mark their composer’s bicentenary.

Crucial to the project has been the involvement, throughout the years of planning and as an inspiring conductor, of the dedicated Wagnerian Anthony Negus. Within the limits set by the necessarily reduced orchestral force of some 60 players that can be accommodated beneath the stage in a pit specially deepened for the purpose, he supplied us with a vivid account of the score. In terms of volume, it could hardly be the end of the world as we know it at the opera’s shattering climax, but there were thrills and moments of exquisite beauty to be savoured along the way.

As with the earlier operas here, I was not enamoured of Alan Privett’s staging which distracted us with three actors-cum-scenery-shifters flitting silently about the stage as the action proceeded. Kjell Torriset’s spartan set, dimly lit by Ben Ormerod, was composed principally of ropes, a large tilting disc and three tube-metal cones on wheels. Perched on the vertiginous heights of these, their bases dressed to form huge skirts, the trio of Norns (Catherine King, Sara Wallander-Ross and Meta Powell) made their appearance; the wonder was they sang so well on their precarious perches.

Vocally, there was much to savour throughout the cast: while Rachel Nicholls’s Brünnhilde, was the stand-out performance, in her Immolation Scene especially, it had a close match for power and seemingly effortless endurance in Mati Turi’s Siegfried, and for precision in Alison Kettlewell’s Waltraud. The entrance of Gunther in a wheelchair was puzzling; the notion that Eddie Wade might have needed it could be dismissed when the device was laid aside as Gunther worked to secure the marriage of sister Gutrune (Lee Bisset) to Siegfried. After an underpowered start in the role of the villainous Hagen, Oxford-based bass Stuart Pendred soon found form.