After recently hosting Dorothy Fields Forever, the King's Head now usefully reminds us of the talents of another legendary Broadway and Hollywood lyricist, Johnny Mercer, even if it's rather uselessly put together (I'm loathe to use the word 'written') by Alvin Rakoff, credited with the book and direction.

These biographical revues are a difficult challenge, I'll allow. Trying to thread examples of the work through anecdotes of the life that created them is a well-worn path, and now that a waspish narrator - in the style of Ned Sherrin, say, for one of the most successful of this genre, Side by Side by Sondheim - is no longer considered sufficient, there seems to be a need to impose some other arbitrary structure.

But you'll actually find out more about Mercer's life, reputation and influence from the brief note on the back of the programme than you'll get from the clunky, between-song scenes that, here, attempt to re-enact, blandly and badly, some of the major events and relationships of the songwriter's life. There's Johnny, a country boy from Savannah, Georgia, arriving in New York and trying to audition as an actor but being accepted as a writer. There's Johnny, going home again to be told his father's bankrupt. Now Johnny's falling in love with Ginger, a chorus girl, and marrying her; and then he meets Judy Garland and falls in love with her.

So far, so lousy; but fortunately, there are the musical numbers to interrupt the relentless storytelling into which they're shoehorned. Mercer never really had any smash-hit Broadway musicals, but he wrote the lyrics to some 1,500 songs - with such composers as Harold Arlen, Hoagy Carmichael, Jerome Kern, Harry Warren and Henry Mancini - that will live on forever.

These include 'Jeepers Creepers', 'That Old Black Magic', 'I'm Old Fashioned', 'Blues in the Night' and 'Accentuate the Positive' . In the spirit of the last, seeking to eliminate the negative and latch onto the affirmative, there are two dazzling performers here to put them across. Andrew Halliday is charged with being the suave Mercer himself, and even if his accent is generic stage American (not the southern drawl the writer would have had, and indeed was once so strong that he was mistakenly voted 'colored singer of the year' during his singing days), he's effortlessly appealing and graceful. So is the lovely Alexandra Jay, now shrugging off her reputation as the West End's most famous understudy to emerge as a singular talent in her own right.

Sadly, Daniel Gillingwater and Sally Hughes, who complete the company, are not in their league. The show as a whole is likewise not up to the songs. Only when it breaks free of its imposed structure for a hurried medley (comprising 14 songs) that it previously hasn't gotten around to, is there finally a sign of what it could have been.

- Mark Shenton