Pirates aren’t what they were. These days they’re likely to be notably unglamorous Somalis who come in speedboats with machineguns to hijack tankers. But 100 or so years ago Barrie was able to imagine one of their leaders as an Old Etonian with a hook for a hand and Robert Louis Stevenson to pass off another as an avuncular- seeming salt with an elongated peg for a leg and a parrot on his shoulder.

But that’s where the trouble begins for Sean Holmes’s uneven revival of Treasure Island. It’s not just that Keith Allen’s parrot is an unmistakably mechanical birdlet that sounds like a Dalek and never goes anywhere near his shoulder, or that his missing limb has become a big brown covering that variously reminded me of a huntsman’s boot, a leather suitcase and an old-fashioned coal scuttle. It’s that, emotionally speaking, his Long John Silver is too much Short John Silver. He’s fly, he’s sly, but he lacks weight and he sometimes contrives to sound like Tony Hancock with a sore throat.

Well, yes, Silver has to end up so incongruously sympathetic that you want him to escape the hangman, but wanted to see more menace and danger behind the spurious geniality. And that’s a special pity, because the evening initially promises to be genuinely scary. Ken Ludwig, who has adapted, doesn’t stint with the ferocious language — “I’m going to squeeze his neck until the pus runs out of his eyes” — nor does Holmes’s cast fail to be sinister.

Tony Bell’s Billy Bones is suitably horrible, as are Paul Brennen’s Black Dog and John Lightbody’s Blind Pew. Indeed, the last of these needs only to substitute a scythe for his clunking cane to become a hellish Death from an ominous medieval mystery play. But the tension flags once the pirates get going. Is it sexist to point out that two of this tiny band of buccaneers are concealing breasts beneath their mariner’s garb? If so, sorry — but it doesn’t exactly add to the terror transmitted by these notably undesperate desperados.

Again, I’d have liked bloodier fights — Michael Legge’s likeable Jim Hawkins gets a knife in the shoulder that does no damage — and a more disturbing Ben Gunn than the blend of Millwall FC skinhead and Eastern shaman offered by (again) Paul Brennen. Also, last night something seemed amiss with the back projections — or were the weird, wobbling shapes that interrupted the images of Bristol harbour, the sea and so on meant to have a touch of Tate Modern?

Behind the refreshingly simple decor — ropes, chests, little more — there’s a band that is far too little-used. But the real problem is a lack of thrills. The language that Allen’s Silver uses to quell a prospective mutiny sums up much. “Shut up you dumb pirates” wouldn’t stop a children’s fancy-dress party getting out of hand, would it? But it’s enough to reduce this lot to, well, children in fancy dress.

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