I promised a review of this, but it will be a brief one, as my brain appears to have died.
The opera is an adaptation by Swann and his librettist, Donald Marsh, from the second volume of CS Lewis' science fiction trilogy. As this is mostly set on an archipelago of floating islands, and the two most important characters spend most of the novel naked (and the fact that the villain of the piece doesn't illustrates his villainy), it will be appreciated that it poses certain challenges to the adaptor, and that's before we consider the fact that much of the action consists of a series of theological arguments and fun and games with translation and semantic inadequacy, followed by a prolonged physical combat between hero and villain (both unarmed).
The opera had a somewhat chequered history; it was not particularly successful in its day, at least partly because Swann's music is resolutely unfashionable - I don't know all that much about music in the sixties, but I was more reminded of Korngold or Walton than anything else. We heard a concert version, with linking narrative, which I must admit I found irksome, especially given the rather pantomime intonation of the narrator (John Amis, a friend of Swann's)†. It gave me a new appreciation for the art of the recitative... Swann and Marsh leave the basic structure of the novel unchanged, though they opens on a note of light comedy as "Lewis" and "Dr Harvard" crash about in Ransome's deserted cottage, by contrast to the novel's opening with Lewis, frightened out of his wits and not sure whether Ransom is telling the truth, insane, or perhaps in league with aliens bent on invading earth.* (The effect of the changes, perhaps unintentionally, was to make Lewis mostly competent and in control, and Harvard the comic relief; whereas novel! Lewis cuts a much poorer figure, and Harvard appears much more professional). There's also a new scene introducing Weston, plummeting towards Perelandra and swearing at the unfortunate technicians at home (Weston is not a nice person, even when he's not crossing Bergsonism with gnosticism or being possessed by the Devil) and the chorus recited his CV - at least, I think that's what they were doing; alas, the acoustics in Keble chapel were so muddy that most of the lyrics vanished under the orchestra.
The orchestration is excellent; the vocal line perhaps less so, though I did wake up with one of the act one duets between Ransom and the Lady embedded in my brain, and there is a spine-chilling solo for choirboy towards the end of the piece, "No man may shorten the way".
The most characterful singing came from Leon Berger, who sang Weston; the other soloists were good enough, but didn't stand out, and I wondered if the choirboy had a sore throat.
It was, perhaps unsurprisingly, a largely American run affair (Lewis' fans seem to be typically American Evangelicals, which is in many ways odd). The tickets gave the work's title as "Perelandra the Opera. Donald Swan's masterpiece, based on the novel by CS Lewis". I somehow suspect an American wrote that....A Telegraph columnist doesn't quite review it here
† Even more unfortunately, during his description of the Green Lady, I had a mental image of Gaila from Reboot Trek, and couldn't shake the association for the rest of the piece. This is really unfortunate.
* As would surely have been the case if this were Doctor Who.