You can forgive a lot on a beautiful summer's evening in Regent's Park's Open Air Theatre, unquestionably the capital's most magical venue. And, I'm afraid, you'll have to forgive a lot with this year's new musical, Where's Charley.

When I use the word new in the context of the Open Air, I mean of course new-old. First seen on Broadway in 1948 and last seen in London in 1958 (with Norman Wisdom in the lead), Where's Charley reaches back to 1892 for its source, Brandon Thomas' quintessentially English farce, Charley's Aunt.

This is a tale of students with servants, women with chaperones and young men harmonising about their salad days at Ivy-covered, sepia-toned Oxford. It's twittishness times twenty, and somehow it just hasn't dated as well or as sympathetically as, say, a really rollicking Gilbert and Sullivan revival. But, while George Abbot's book detailing marriage contracts and finagled fortunes is hard to digest according to 21st century appetites, it's Frank Loesser's lyrics which sound particularly old-fashioned and inane - comparing a lover to a frightened "starling" in order to rhyme with "darling" springs to mind.

The cast also seem uncomfortable - and slightly under-rehearsed - with this ill-fitting production, directed by Ian Talbot. There are no real stand-out performances, although Cameron Blakely as cross-dressing Charley is rambunctious enough, wringing laughs from his fictional aunt's deflection of aging suitors and repetition of the one-liner "Brazil, where the nuts come from".

Elsewhere, the males of the company are pretty uniformly lacklustre and certainly outperformed in the vocal department by their female counterparts, of whom Lottie Mayor as Charley's love interest Amy fares best at capturing the prim ladylike bemusement of the era without grating at the same time.

Carping aside, there are some real treats to be found here. "Make a Miracle", in which Amy and Charley contemplate their romance in the face of exhilarating turn-of-the-century technological process, is very sweet. And "Once in Love with Amy" remains a lovely and irresistibly hummable tune, enhanced visually here by Blakely's lively tap routine.

Nevertheless, in the memorability stakes, the score's poverty is stark compared to last year's Open Air revival, G&S's The Pirates of Penzance, which returns this summer with a new cast. Where's Charley also loses out to Pirates for good fun and sheer exuberance.

Still, when the weather's fine and the venue weaves its spell, forgiveness comes easier. If you lower your expectations and follow the advice dispensed in one of the show's numbers, "you'll like it more the further back you stand".

Terri Paddock