A chorus of Disapproval, Harold Pinter Theatre, London / Jesus Christ Superstar, O2 Arena, London

Alan Ayckbourn's play within a play seems under-rehearsed, while 'Superstar' is still entertaining on its umpteenth coming

Alan Ayckbourn’s play within a play seems under-rehearsed (Geraint Lewis)

It starts with the finale. In the opening scene of Alan Ayckbourn's A Chorus of Disapproval – his 1984 seriocomedy revived by Trevor Nunn – a throng of 18th-century doxies dance round a grinning rascal in a periwig (Nigel Harman). He has just been saved from the hangman's noose. Everyone sings in celebration, followed by a curtain call and loud (pre-recorded) applause.

Then we see – behind the curtain – the post-show reality. The scene was from John Gay's Beggar's Opera. Harman's Guy was playing the rakish Macheath, but now he changes miserably out of his period costume, cold-shouldered by others in the company. One wonders why.

A Chorus of Disapproval goes on to explain by tracing Guy's backstory from the day he joined this small-town amateur operatic society. Auditioned by the group's director, Rob Brydon's chummy Dafydd, Guy seems mousy and nice. Almost curled up with shyness, he smiles politely as other society members assault him with bad advice or wanton come-ons. However, as he is promoted from bit part to leading man, he begins two-timing and breaking hearts.

Ayckbourn has enjoyed a phenomenal comeback in recent years, but A Chorus of Disapproval is not his most brilliant work. Written at speed, jerry-built almost, its subplot is scrappy, and the art-life parallels rudimentary – 18th-century ballads about womanising slung among scenes of modern-day permissiveness, loosely justified by the framework of rehearsals. The piece suffers by comparison with Michael Frayn's Noises Off and Tom Stoppard's The Real Thing.

A good production could conceal the structural weaknesses by bringing out psychological complexities. But Nunn's cast seem under-rehearsed, sometimes outstanding, sometimes ropey. Might the director have been distracted by having another production in the offing – Sam Beckett's All That Fall – with its first night in two weeks' time?

Harman's widowed Guy may well gain depth as the run progresses. He and Ashley Jensen's Hannah (Dafydd's uncherished wife) are extraordinarily touching when they fall in love at first sight, with quiet ardour. Yet elsewhere beats are missed which could otherwise have made Guy a more intriguing dark horse, introducing glimmers of doubts about his innocence. As it stands, his claim that he "loves" Daisy Beaumont's swinging, slutty Fay, as well as Hannah, merely seems improbable. Beaumont's performance is not at fault. She deftly steers just clear of caricature, and Brydon is impressive as well, effortlessly naturalistic and comic.

The problem is, though, among the lesser supporting roles it's sometimes hard to distinguish the send-up of am-dram woodenness, when in rehearsals for Gay's romp, from plain bad acting.

Unlike Macheath, there is no reprieve for the Son of God in Jesus Christ Superstar, the celeb-cast revival of Andrew Lloyd Webber and Tim Rice's Seventies rock musical, now on a national stadium tour. Played by television talent-show winner Ben Forster, Jesus dies in agony, strapped to the bars of a lighting rig that has swung down to form a gigantic blazing crucifix, with no ensuing resurrection. The O2 Arena, where I caught the show, is surely some inner circle of hell with its endless queuing. Plus the on-stage band was so malevolently over-amplified that invisible demons appeared to be shaking my seat throughout the first half.

Mercifully, the volume was turned down at the interval, allowing Laurence Connor's production to emerge as a startlingly successful cross between theatre, film and rock gig. Christ's authority-challenging disciples are 21st-century scruffs with dreadlocks and tattoos, shacked up in tents evoking the Occupy movement. Their struggles are relayed, simultaneously, on a vast screen, like 24-hour news, overlaid with tweets when they chorus "What's the buzz?" The ex-Radio 1 DJ Chris Moyles is only mildly amusing playing Herod as a smarmy game-show host (inset, left), but Melanie C's pained Mary Magdalene sings with real feeling, while Forster and Tim Minchin's Judas Iscariot rage at injustices and each other with electrifying, almost punk ferocity. It may not have everlasting life, but Jesus Christ Superstar is, amazingly, hardly showing its age.

'A Chorus of Disapproval': (0844 871 7622) to 5 Jan. 'Jesus Christ Superstar': (jesuschristsuperstar.com) to 21 Oct