Mr Jackson has also launched two digital channels, Film 4 and E4, although neither has yet broken even. Next year, Channel 4 will launch a racing channel with interactive betting.While his predecessor, Michael Grade, was dubbed "Britain's pornographer in chief" by the Daily Mail, with Sex and the City, So Graham Norton, and other programmes, Mr Jackson consolidated Channel 4's reputation for extending the boundaries in sex and sexual innuendo. He also oversaw the coming of age of reality television with Big Brother.Few in the industry could have foreseen the direction in which Mr Jackson was to take Channel 4, which he took over in 1997. But now that he is leaving British broadcasting – to take up a job in US television – it is testimony to Mr Jackson's achievements that his successor will find his record such a tough one to emulate.An intellectual, he had made his mark as head of BBC2, taking charge of The Late Show and many other arts programmes. After that, as controller of BBC1, he was responsible for screening the acclaimed version of Pride and Prejudice and commissioning the landmark drama Our Friends in the North.But at Channel 4 he ceased to be such an aesthete, and showed his business and aggressively entrepreneurial instincts. He poached Test Match cricket from the BBC, relished bidding against Sky for rights to American imports such as Friends, and showed ever more risqu?aterial.Queer as Folk, Britain's first gay drama, was screened on Channel 4, and received more viewer complaints than any other programme on television.

It was censured by the regulators for the "celebratory tone" of its portrayal of under-age gay sex.In the US, Mr Jackson is taking up a position as president and chief executive officer of the USA Entertainment Group, the film and television production arm of USA Networks, reporting directly to its chief executive, Barry Diller.He will take charge of several cable channels, including USA Network and the Sci-Fi Channel. He will also be responsible for a television production house, Studio USA, and a film studio, USA Films, which produced critical and commercial successes such as Traffic and Being John Malkovich. But it is likely that Mr Jackson will one day return to Britain. He was mentioned as a candidate for the post of BBC director-general when Greg Dyke got the job, and is likely to be mentioned again when Mr Dyke stands down.Channel 4 swept the board at this year's Bafta awards, winning 11 of the 19 awards, more than the BBC and ITV combined. The channel, funded by advertising, overseen by an independent board and guided by its original charter, has been cited as a model for public service broadcasting.But, equally, critics have been worried that Mr Jackson has deserted the channel's roots as a broadcaster of experimental programmes offering a radical alternative to mainstream broadcasting. It was hard to see, for example, how buying the services of Richard and Judy from ITV helped to extend the boundaries of broadcasting.David Elstein, the former head of Channel 5, recently told the Royal Television Society: "Channel 4 has more money than it needs. Its revenues exceed its programme budget by £250m a year; last year, it increased overheads by 30 per cent and staff numbers by 20 per cent It pays spectacular wages and offers state-of-the-art perks.

Basically, it's a runaway train where the non-executive directors seem to have lost the plot."Vanni Treves, the Channel 4 chairman, said last night: "Michael took charge at a time of huge uncertainty, with the channel barely having started preparing for the arrival of digital TV or having considered the impact of other new technologies, such as the internet."He has embraced this challenge and the transformation under his leadership has been total, with Channel 4 now widely acknowledged to have the most effective cross-platform strategy of any UK terrestrial broadcaster," he said.Mr Jackson said last night:"Channel 4 is a unique and wonderful organisation and anyone would relish the challenge of leading it My next challenge ... is to lead a major group of media assets, marrying mass and specialist interests, and I am excited by the prospect of operating in a new market." Michael Jackson: the good times and the badHitsBig Brother: In the week in which one of ITV's Survivors will walk off with £1m, all the talk is of Big Brother. While Survivor was cut back to one episode each week, Big Brother has regularly scored four million viewers.Test Match Cricket: C4 moved away from the traditional BBC format to aim its coverage at a younger audience with experimental and visually exciting techniques.So Graham Norton: The channel took a risk on the risque Irish presenter who has since become the lynchpin of its Friday night schedule. The BBC opened its chequebook earlier this year to try to tempt him away ­ with no success.MissesAnna Karenina: Despite an enormous promotional campaign, David Blair's adaptation of Tolstoy's classic novel proved to be a big-budget flop.