If South Park sniggers at modern America, The Book of Mormon is more warm-hearted, weaving unlikely redemption out of a send-up of credulity. Leaps of faith, it tells us, are absurd commitments. That is no reason not to make them. The only downside is that the West End's other musicals look pallid by comparison.

A more sedate evening is on offer round the corner at the Gielgud, where Peter Morgan's The Audience reprises Helen Miren's spookily fine portrayal of the Queen in the film drama, in which Her Majesty did battle with Tony Blair's government in the wake of Diana's death. In this sequel to Morgan's monarchical study, we see HRH through the prism of her weekly audiences with prime ministers from Winston Churchill to David Cameron.

The result, directed by Stephen Daldry, is assured and the critics have largely lapped it up. It begins with an elderly Churchill (Edward Fox a late substitute for an indisposed Robert Hardy), hectoring a young Queen who speaks Enid Blyton English but already possesses sharpness and determination. 

Both the heroine and the play get into their stride when she encounters Harold Wilson (an artfully rumpled Richard McCabe), who finds chilly Balmoral a trial and teases her for her eccentric Hanoverian heritage, while impressing her with his meritocratic clout. Part of Mirren's success in the role is her ability to mould her posture as well as her features into an uncanny resemblance of a woman whom so many have tried unsuccessfully to capture. The Queen is represented as a stoic, unknowable figure, a touch on the obsessive-compulsive side when it comes to shoes and pens and wedded to a duty which, the play suggests, must feel like a chore without being revealed to be such.