The "roast" is an odd American phenomenon, a sort of testimonial showbiz party during which the guest of honour is mercilessly insulted by fellow celebrities. The tradition began at the Friars Club in New York and was televised as part of The Dean Martin Show in the 1970s, and more recently on Comedy Central. Now Channel 4 is bringing us a British version, Comedy Roast, with Bruce Forsyth as last night's inaugural dishonoree. Jimmy Carr, Jonathan Ross, Jon Culshaw and Jack Dee were among his genial tormentors - a "Who's Who of who was available," as Carr said. It looks as if they went through the Js of some publicist's email address book.

There's a problem with insulting Brucie: it's hard to get beyond his age. "When the dinosaurs died out he was taken in for questioning," said someone. "He's seen Halley's comet three times," said someone else. A lot of the jokes overlapped. Variations on "Nice to see you, to see you nice" abounded. Jonathan Ross said "fuck" a couple of times, but the whole thing lacked the sleazy exuberance of the original format (you can watch the Dean Martin ones on YouTube). Only Bruce himself seemed to catch the spirit of the thing. "That was funny," he shouted at Jack Dee. "I knew you'd make me laugh eventually."

In a merciless variation on a tribute show, a host of comedians and celebrities line up to lampoon Sharon Osbourne. At the start, the host Jimmy Carr compares her to the Queen. "Her children are dysfunctional. Her husband is incoherent and nobody is really sure what she does." Thereafter, the likes of Alan Carr, Ronni Ancona and Louis Walsh take to the podium and let rip about her age, her plastic surgery, her husband, her incontinent dogs, her foul mouth and her fashion mistakes, while she sits at a table and cackles loudly. The highlights of the evening are Ancona reading extracts from Osbourne's new novel, Revenge, and Patrick Kielty risking his life to mock her parenting skills. "What a delightful evening it's been," says a glum Jack Dee.

My reviewer's DVD of the first of Channel 4's enterprising Comedy Roast was incomplete. It lacked a title sequence and, at the end, a caption read "CRAWLER CREDITS". But there were no crawlers to credit. Perhaps for the first time on British television the showbiz mafia came not to praise but to bury one of its godfathers. Still, as with the best man's speech, the tone is hard to get right. On The Larry Sanders Show the fictional chat show host was rendered suicidal by his friends' merciless "tributes". You don't want that. But you do want some of the barbs to hurt.

Bruce Forsyth's age was a subject of jokes back in his 1970s heyday and, even though, at 82, they are rather more acute now, they are still more affectionate than cruel. Jimmy Carr, the show's MC, led the way with them - Brucie was the first in his community to walk upright and use tools etc - but it was Jonathan Ross who took on Forsyth's real vulnerability: his marital record. Doing a passable Brucie impression, Ross mimicked him saying "I've told my wife we are working late, so we have ten minutes for a quickie, Anthea." Anthea Redfern, The Generation Game's lovely hostess, was to become, younger viewers may not know, the second, but not last, Mrs F.

He was not thanked for his efforts, even though Wilnelia Forsyth, herself, pointedly mentioned her husband's three wives. It was a deadly reminder of how lonely it is when you fall from favour as Ross, following the Andrew Sachs debacle, clearly has. Sean Lock was surprised Ross had turned up in person "because normally if you want to insult an elderly national treasure, you do it on the phone". That was good but it was Forsyth himself who did most damage. Eric Morecambe would have ripped into Ross ("I am sure he would," said Ross glumly). Ross was "all washed up and not even 50"£. The Ross-hating press has been accused of hyping Forsyth's attack but I think Ross had got to him, and for that he should be congratulated. A well-concealed side of Forsyth was briefly exposed.

Last Night's Television: Bruce Forsyth: A Comedy Roast

The point about a comedy roast - spectacularly missed by the newspapers who indignantly reported on Jonathan Ross's insulting remarks about Bruce Forsyth recently - is that the guest of honour is on the spit. An essentially American institution, in which showbiz entertainers gather for what the Scots would call a flyting - or an insult contest - the whole idea is that you let them have it with the best you've got. Offence and embarrassment don't have an invitation, since the only breach of good taste at such events would be to serve underarm because you thought the recipient couldn't handle anything tougher. What's really interesting about them, though - apart from the occasional pre-prepared aces - is that embarrassment is always lurking about there somewhere, waiting to pounce on the possibility that a friendly insult might have strayed just a little too close to a nerve. And in the first of Channel 4's Comedy Roast's it looked to me as if embarrassment was spending quite a lot of time near Jimmy Carr and Jonathan Ross.

It's a fate you wouldn't wish on your own worst enemy: Bruce Forsyth must have done something very bad in a former life to have his recent gruesome grilling by Piers Morgan, a man who insists on probing where no one wants to go, swiftly followed by the undercooked fawn-fest that was Bruce Forsyth: A Comedy Roast.

Starting with the dreaded words 'please welcome your host... Jimmy Carr!', a phrase guaranteed to have me instantly gagging (but not in a good way), C4's resident Smug MC, a ventriloquist's doll in human form, launched into his unique brand of makes-you-want-to-slap-him charm. 'A roast is like good-natured bullying,' he smirked. 'Good-natured in that it's happening to someone else, not you.' Unbelievably it was downhill from there, a gruesome selection of backslapping/stabbing blokes taking turns to out un-funny each other. Jonathan Ross started off with his tired effing and blinding routine, clearly miffed he wasn't talking about his favourite subject (himself). No, he was there to dishonour Bruczie, so what did Ross's rapier-like wit conjure up? No idea, it was instantly forgettable, other than setting up the night's weary theme: wow, Bruce Forsyth is, like, really old. He's done lots of dodgy gameshows. And he's got a chin. And a beautiful wife. Satire it wasn't.

Jimmy Hill's chin twin guffawed through gritted teeth throughout, taking it on the proverbial. But his lizard-like stare needed double-glazing to get through the kill-the-room combo of Bruno Tonioli and Arlene Phillips, whose contribution was up there with such classic double acts as Sam Fox and Mick Fleetwood and Rula Lenska and George Galloway for making you want to stab your eyes out.

All this crackling-free, toothless 'roast' proved was that the more people ho think they are funny there are in a room, the less likely you are to have a laugh. Only Sean Lock emerged with dignity intact but his best line - a dig about being surprised that Ross turned up in person instead of persecuting a national treasure by phone - was all over the trailers, so you'd heard it anyway. Next up it's Sharon Osbourne then Chris Tarrant - truly, C4, you are spoiling us.

A comedy roast is a prolonged mickey-take of someone while that someone is still in the room to enjoy the jokes, but from the very first of Jimmy Carr's opening remarks it's clear Sharon Osbourne has her work cut out. The jokes are savage and the language is terrible, as Patrick Kielty, Alan Carr and Jack Dee rip into the former X Factor judge's parenting skills and plastic surgery.

Like a best man speech for a celebrity, the roast - where a famous guest of honour is mercilessly insulted by other celebs - is a long-standing ­tradition in the US. Channel 4 has imported the concept and tonight it's the turn of Sharon Osbourne - a human equivalent of an open goal.

Hosted by Jimmy Carr, this is the funniest and also the rudest hour of TV all week, with Jack Dee, Patrick Kielty, Gok Wan, Alan Carr, Louis Walsh, Ronni Ancona, Keith Lemon and Elton John paying acid-tongued tribute to Sharon's extensive plastic surgery, mothering skills and propensity for sending dog poo to her enemies.

And this put-down from Patrick Kielty shows that nothing is too near to the knuckle. "It's fair to say that Ozzy has never strayed," he quips. "He did once make a dash for freedom but after Sharon cut the brakes on the quad bike, he's now learned his lesson..."

Last Night's TV - Bruce Forsyth: A Comedy Roast

No turn was left unstoned, even Bruce's wife Wilnelia came in useful as a gag target for Manford, Carr et al, but she too managed to retain her dignity while all about her, juvenile jabbers were waving theirs goodbye. So will I be tuning in for any further helpings of 'roast'? That would be a no.

Review - Bruce Forsyth: A Comedy Roast

A couple of decades ago, TV royalty used to be rewarded for long service with a good-natured love-in on This Is Your Life. Not any more. This being the 21st century, the celebration has to be tempered with a smattering of sneering sarcasm and Jimmy Carr one-liners.

A "roast" in this instance is a kind of good-natured ragging session: the elderly golfing enthusiast is mocked by a panel of comedians, all of whom seem as perplexed as he is as to what they're doing there. Jimmy Carr, not a performer known for his amiability, is the master of ceremonies, seemingly on his best behaviour while a panel including Jack Dee and Barry Cryer share their Brucie-based reminiscences.