Follow My Leader, Repertory Theatre, Birmingham

Alastair Campbell recently revealed that the one drawback with England's President was his tendency to play the guitar while talking on the phone. Personally, I'd love to experience this phenomenon. It must be like being on the line to a (very holy) cross between Roger Whittaker and a wannabe Nobel peace-prize laureate.

Tony Blair gets more than the chance to strum some strings in Follow My Leader, for here he becomes the star of a scathingly satirical new musical. Having dissed Campbell in the hit-and-miss Feelgood, Alistair Beaton now provides the book and the lyrics for this hit-and-miss tuner, in which the hits come faster and more accurately targeted, as an overlong evening and a talent-packed but not yet tight production run their course.

A look at the diversity of the roles covered by one of the performers, Sevan Stephan, will indicate how wide-ranging the show aims to be. The actor performs (and sings and dances): a vicar; a Guantanamo prisoner; an Iraqi newsreader; an embedded reporter in the invading army in the war on Iraq; Clare Short in her most maddening resigning-when-it's-too-late mode, and an anti-American singer.

Blair's co-star is, of course, George Bush, and the piece takes the virulently anti-Christian line that the pair pose a threat to the planet principally because of their firm belief that they have a special relationship with God as well as with each other. The Prime Minister, played by Jason Durr with brilliant timing and an extraordinary feel for the combination of Bambi and megalomaniac in the man, thinks that his hot line to the Deity is quicker and more personal. And indeed, God does check into the musical to give Blair his mission to be a "restraining influence" on Bush. The story of the show is how the PM winds up doing the reverse because he wants a place in the history books, and history is written by human victors, not by the Gods they serve.

Most modern musicals navel-gaze. This one has almost the opposite fault. It takes us from the comic double-act of spin merchants in the Pentagon, to footage of peace marches in Britain; from Guantanamo Bay to the fjords of Norway where some deranged neo-Con hunts weapons of mass destruction. There are many inspired ideas. Converting Chemical Ali into Comical Ali and making him Campbell's gung-ho replacement is as deliriously droll a notion as having Blair endeavour to explain his foreign policy to baby Leo. There's an authentic chill, too, to the depiction of Bush's private contempt for the PM and Britain.

But in throwing every musical style and gag they can think of at the problem, the makers allow the show to lose focus. And its spirit sometimes sours and descends too far below the belt. It could lose three quarters of an hour and be better for it. After all, if your target is the global damage caused by the vanity of Bush and Blair, it is better not to expose yourself to the charge of self-indulgence and overkill.

To 10 April (0121-236 4455); then Hampstead Theatre, London NW3 (020-7722 9301) 21 April to 15 May