Old Roman joke: "That slave you've sold me has just died." "My God, he never did that when he belonged to me!" Ah well...perhaps you had to be there...and by "there", I mean a tavern somewhere in the Suburra around 40BC, because the gag didn't exactly bring the house down in Michael Grade and the World's Oldest Joke.

In fact, it died, along with a startling number of other historical jokes and quite a few contemporary ones, the producer of this otherwise intriguing exploration of the history of the rib-tickler having taken the perverse decision to give the job of telling the gags almost exclusively to people who weren't very good at it. What Michael Grade was interested in was the embedded human need to crack wise. What the director seemed to be interested in was getting in the way as often as possible, quite often with members of the public mangling perfectly blameless jokes.

To be fair, it was hard to imagine anyone being able to revive some of these vintage gags. Take this, from a Tudor compilation of humorous quips - Q: What is the cleanliest leaf? A: The holly leaf, because no one will wipe their arse with it. Or the jokes that depended on the reliable hilarity involved in beating your wife. And once the programme had calmed down a bit - and got away from the philosophising about the nature of comedy that also bogged down the opening - it proved interesting. It was good to learn about Poggio Bracciolini, a papal employee who compiled the Liber Facetiarum, an early joke book full of stuff that only a cardinal could read without blushing. And I liked the revelation that the Greek passion for lettuce gags was dependent on the belief that it was an aphrodisiac. Substitute Viagra for the little gem and most of them would (half) work now. The oldest joke in the world, incidentally, was a fart gag, which seemed somehow comforting. A warm, gently rising fug of carnality.

The former chief exec of Channel 4 goes in search of the origins of the joke and attempts to discover its earliest example. So he starts in Liverpool with comedy legend Ken Dodd. Trawling history for evidence of what tickled our ancestors, Grade discovers it was basically the same mother-in-law gags and references to anal wind we all love so much now. Interesting contributions come from Tim Vine and the ever-sharp Barry Cryer. Seriously, he must sleep in an amber cave.

A jape, a jest, a gag, even a jewel or trinket in Old English. There are many ways to describe a joke, but pinning down why a joke works is about as easy as nailing jelly to the wall.

Here the jovial Michael Grade does a pretty good job of getting that jelly on the wall - with the help of esteemed gagmeisters Ken Dodd, Barry Cryer and Tim Vine.

His scholastic peregrinations in search of the world's oldest known joke prove we've always laughed at the same things - except we're not so fond of lettuce and herniated eunuch gags nowadays - while the scholarly analysis is tempered by a barrage of one-liners.

What makes the best joke?

"The joke is therapy, a momentary escape from the hundrum of life or, in some cases, the sheer misery or even horror of it," says Barry Cryer.

A shame that what could have been an entertaining foray into the history of joke-telling should be so lacking in humour. There's nothing inherently wrong with the premise of the documentary in which Michael Grade asks whether there is such a thing as a new joke or whether we are laughing at the same things our ancestors did - it's just that it's all a little boring. Ken Dodd, Barry Cryer and Tim Vine are among those pointing the way as Grade discovers what Romans and Tudors found funny, why lettuce was once thought amusing, why a 14th century papal secretary was responsible for one of the first joke books and why the BBC once censored some jokes - chambermaids and lodgers were among the banned topics.