The Donkey hasn't quite hit its stride as it limps into a second episode, brandishing a hidden camera like it's a refreshing idea. Attempting to buy a kidney off a hairy man, persuading unwitting strangers to administer first aid with a steam iron, and hassling key cutters for a gold one with a pointy end are good ideas in principle, but these are all jokes that never quite seem to get to the punchline. With over-the-top voices and sketches that go on too long, the result is largely a mirth-free affair.

If you listen carefully to the last 15 minutes of this second episode, you can hear the sickening sound of the hidden-camera barrel being scraped clean. Whereas many of this show's antecedents understood that fly-on-the-wall comedy works best in short bursts, each of the sketches here drag on far beyond their natural life.

This week we follow another bunch of Glaswegian and Liverpudlian 'characters' interacting with unsuspecting members of the public; some of the skits have legs, but the best ones are put aside in favour of irritating voices and pratfalls. A scene where a woman tries to persuade a man to give her a kidney almost raises a smile, and there's a nice sight gag involving a polaroid camera, but each ends up outstaying its welcome.

Trojan Donkey's first episode perfects the hidden-camera formula with overdone accents, toilet humour, and even a rugby lad forced to recite a Rudyard Kipling poem in ridiculous surroundings. But, despite the best efforts of comedian PJ Gallagher and characters like the Cowboy Builder, this is a one-trick donkey: a revival of the Trigger Happy/Fonejacker premise which will entertain without adding any new quirks. Gallagher fronted a similar show called Naked Camera in Ireland, but this rehash seems unlikely to win him as many plaudits.

How will a tattoo artist respond to a request to copy the whole of the Bible on to a punter's back? And will a legitimate builder be persuaded to lend a jackhammer to a self-proclaimed 'cowboy' to chip his mate out of a block of cement? In this hit-and-miss comedy sketch show, ordinary folk are 'pranked' by a team of hidden camera japesters. Kudos to the lad on the bus who's definitely not Peter Andre but can't persuade 'celebrity stalker' Ursula.

All hidden camera shows need a USP. Trigger Happy TV had a man with a big telephone. Off Their Rockers had old people being rude. Trojan Donkey? A man with a funny voice. Diminishing returns...

It's really hard to see how this new series got commissioned, other than that it's presumably incredibly cheap to make. The format feels played-out, the humour one-dimensional and the mediocre scenarios are returned to again and again. For example, celebrity stalker Ursula might have got away with mistaking a young bus passenger for Peter Andre if the sketch had been a minute long. It might even have raised a smirk. But back we go, time and again, until the joke's been hammered to death.

Trojan Donkey finds itself in the post-pub slot. But you'd have to be seriously well-refreshed to give this more than five minutes.

This is a simple, old-school, hidden-camera prank show adapted from an Irish series and given a new name. A man talks to a bemused plumber in a high voice complaining about the "whoooosh!" noise his toilet makes. A woman accosts a fellow passenger on the bus claiming to recognise him as Peter Andre. A workman claims to be a "cowboy builder" whose mate has got stuck in cement.

They're slight ideas that shouldn't work as well as they do, but the performers are just convincing enough, and some of the victims' reactions are wonderful. I loved the patient-but-firm tattoo artist trying to convince a man who wants the whole Bible inked on his back that it'll never work.