I have no objection, in principle, to people touching up Gilbert and Sullivan. But Ian Talbot's otherwise enjoyable production is hindered rather than helped by Herbert Appleman's revised libretto which turns Dick Deadeye into a choric figure busily explaining the objects of Gilbertian satire.

Tim Brooke-Taylor did something similar at a recent Prom but that was a concert performance. And, while it is helpful to know that the joke about a landlocked First Lord of the Admiralty was based upon WH Smith, much of the information here is either patronising or redundant. The show descends to Jackanory level when it tells us that Victorian tars were free-swearing roughnecks rather than polite gentlemen or that Gilbert and Sullivan parodied music-hall and Italian opera. By drawing attention to the age difference between Captain Corcoran and Ralph Rackstraw, famously swapped at birth, the show also punctures the deliberate absurdity of Gilbert's climax.

That aside, Talbot's well-cast production has a genuine air of festivity. It is a real treat to see Desmond Barrit, with his Roman profile and stately embonpoint, as the upwardly mobile Sir Joseph Porter. Scarlett Strallen as his intended, Josephine, combines a good voice with kittenish charm, particularly when clad in a catsuit. Sirine Saba makes a genuine character out of his predatory cousin, Hebe, by turning her into a hornrimmed husband-hunter. And, when he's not underlining what's already in italics, Gary Wilmot is a likeable Dick Deadeye.

At its best, the show even achieves that touch of ecstasy that is the sine qua non of all good musicals. Predictably, it comes here with Never Mind the Why or Wherefore which, at its second encore, is sung and played at breakneck speed. And throughout Catherine Jayes directs the nine-strong band with committed fervour. On a fine night there are few more pleasant ways of spending a London evening. I just wish Mr Talbot had heeded Sam Goldwyn's advice, to a revisionist Hollywood scriptwriter, to "take out the improvements".

· In rep until September 10. Box office: 0870 060 1811.