Not the Messiah (He's A Very Naughty Boy), Royal Albert Hall, London

And now for something completely different? Well, yes and no; swings and roundabouts, square pegs and round holes, know what I mean, nudge, nudge. Eric Idle and composer John Du Prez have already conquered Broadway and the West End with their stage musical version of Spamalot. But on Friday – to celebrate the 40th anniversary of the first Monty Python broadcast – they presented a one-off performance of a piece that is just a smidgen more megalomaniac.

Not the Messiah (He's A Very Naughty Boy) is a comic Handel-spoofing oratorio version of The Life of Brian, the controversial 1979 movie which satirised blind faith and the underhand wiles of Christian zealotry through the fate of the hapless mixed-race Brian Cohen, a nobody who is mistaken for the Messiah, becomes a reluctant revolutionary with the Judean People's Front and winds up nailed to a cross.

The fans (and they packed the place to the rafters) received it rapturously, but then I reckon that they would have blown the roof off even if the surviving team members (excluding John Cleese) had sent along their bow tie-sporting fridges as stand-ins rather than turned up themselves. And who am I (as a selective admirer) to knock the fun enjoyed by the greying faithful (and their remarkably compliant kids). I enjoyed the ravishing silk-bristled texture with which the BBC Symphony Orchestra (in fantastic form, throughout, presumably for a considerable fee) performed "Liberty Bell", the Python theme-tune at the start. And I liked the way Michael Palin (during the encores) unsheathed himself from his drag clobber as Mrs Betty Parkinson to emerge as a fully-formed lumberjack for an (oddly ropey) rendition of that song. Also, dull would he be of soul who failed to experience a bit of a thrill when the entire audience waved their candles in time to cheery old "Bright Side of Life".

So how did I feel the rest of the time? Sick as a dead parrot? No; lonely mostly and a little mystified. The essential difference between the mediocrity of Not the Messiah and the fitful genuinely hilarity of the stage Spamalot is that Idle and Du Prez understand the genre of musical comedy and so can have spirited fun mixing Holy Grail and Broadway-reaching ambitions. But while they may appreciate the concert hall protocols of oratorio, they don't comprehend its deep conventions. And in any case, what would satire in this area be subverting? Life of Brian is an attack on mindless worship, not the faith itself. I take no joy in saying that this immense event reminded me of nothing so much as Florence Foster Jenkins, the notoriously tone-deaf American socialite who used to hire the Carnegie Hall at her own expense for her vanity caterwaulings.