POOR old Bridget. England’s most lovable, accident-prone thirtysomething has lost none of her fabulous knack for shooting herself in the foot. The ace reporter is still skydiving into pig pens.

For six glorious weeks “and 71 ecstatic shags”, her love life with the sex-god Mark Darcy has been well-nigh perfect. Yet the old insecurities are alive and well. “What happens after you walk off into the sunset?” Bridget ponders one morning. And exactly what is the nature of Darcy’s relationship with his nubile secretary?

Pure suspicion fuels this whimsical sequel, which is fat with comic setpieces but spookily thin on real substance.

Renée Zellweger heroically plumps up again as Bridget, but this Bridget is beginning to look decidedly past her shelf life, with a puffy face in need of a health farm. The breasts resemble pillows, the awful jumpers are more shockingly pink, and the wobbly bits are wildly out of control.

In stark contrast, Colin Firth’s poker-stiff lawyer has never looked more trim or, indeed, tight. The chances of him popping the question might be shrinking. That Darcy will not, in Bridget’s neurotic imagination, stand up and fight for her is evidence enough for their first serious bust-up.

All the old admirers are also back in force. But their persistence is beginning to wear in Beeban Kidron’s sequel.

This wouldn’t be a proper Bridget Jones film without Hugh Grant’s smooth-talking bastard, Daniel Cleaver, up to his old tricks. Having reinvented himself as a TV travel pundit who sleeps his way around the hot-spots of the world, Cleaver does his best to creep back inside Bridget’s giant grey knickers. Taking advantage of Bridget’s loss of faith in Darcy, he sweeps her to Thailand for a session of sweet-talking that would make Rasputin blush. It’s a film-stealing cameo by Grant in which he doesn’t break a bead of sweat.

To crank up the increasingly bizarre drama, Bridget is arrested in Bangkok airport while inadvertently carrying a kilo of cocaine in her suitcase. Left for dead by Cleaver, Bridget is banged up in a Thai prison facing 20 years.

Cue the world’s most anal international lawyer, Darcy, who gallops to the rescue while our Bridget teaches a vast cell full of Thai prostitutes how to sing Madonna’s Like A Virgin. It’s a mad and preposterous warm-up for another Cleaver v Darcy boxing match around the Serpentine Gallery that is, admittedly, a joy to behold. But the getting there is a stretch too far, even for the writing might of Richard Curtis and Helen Fielding.

Zellweger still inspires affection as the hapless fantasist, but even she can’t make the comedy sing. The flatulent plot doesn’t flatter her feckless charm. It’s the staples — the ghastly in-laws, the Christmas party, the posh dos with dumbstruck crusty judges and baffled ambassadors — that rack up the romantic-comedy points. I fear that fans will be disappointed.