Lord Birt, the prime minister's "blue skies thinker" and former BBC director general, last night challenged the "tabloidisation" of British intellectual life and said the media had become too reliant on "easy cruelty" and "the desire to humiliate".

Delivering the keynote MacTaggart lecture at the Media Guardian Edinburgh international television festival, he seized on the trend for celebrities to front documentaries and factual programmes.

"Let us not tabloidise our intellectual life. Let's skew the balance back towards scholarship ... Leave the celebrities for the jungle."

Picking up the threads of arguments he has doggedly sustained throughout a career that took him from LWT to the BBC, he called for "more truth and beauty" in broadcasting.

Lord Birt claimed that the media was still too superficial in its political reporting and "obsessed not with policy but with personality". And, in a criticism that echoes those elements of the Labour government who blame the media for the surge in political apathy among the electorate, he said he was "weary of cynicism".

"Public service broadcasting would serve the nation better if it shifted the balance of its political journalism towards depth of analysis; towards insight and substance; towards honest, patient inquiry."

He also singled out television drama for criticism. He said that while drama was "perfectly professional", much of it was uninspiring and unfulfilling. Viewers now had to look to the cinema for "the raw author's voice" in films such as Alex Payne's Sideways and Paul Haggis's Crash.

"Today's drama practitioners ought to rent a great skip and throw away the stereotypes and the formulae," he urged, in his first major speech on broadcasting since he left the BBC five years ago.

Twelve years after the late Dennis Potter stood on the same podium and lambasted Lord Birt as a "croak-voiced dalek" who was destroying the soul of the BBC, the peer used the speech to draw a comparison between his contribution to the corporation's legacy and that of its founder, Lord Reith.

Given the pace of technological change and the impending shift to digital TV by 2012, he identified an "intensifying threat to the UK's extraordinarily successful tradition of public service broadcasting".

He predicted the death of ITV as a public service broadcaster "in any meaningful sense", in a world where it was losing share to multichannel rivals. Meanwhile, Channel 4 would need financial help to face "a tide that cannot be held back" - likely to be taken as a coded argument for the BBC to share its licence fee with C4.

Laying out his policy vision to preserve public service broadcasting in a multichannel age, he warned that Channel 4 faced extinction unless policy makers came up with a radical new model to fund it.

He called for a "brand new model" to sustain public service competition with the BBC in the digital world. Lord Birt said that the corporation "has at times become transfixed by its commercial competition and paid insufficient attention to the need to serve its many different audiences".

Lord Birt led the BBC for eight years from December 1992, during which time he faced criticism for his management style, but was also seen as securing the corporation's legacy with a generous licence fee settlement and the launch of digital channels and websites.

Last night, he boasted of "taking a bloated and wasteful institution and halving its costs in 10 years", "positioning the BBC for the digital age while other broadcasters dozed" and persuading Margaret Thatcher not to break up the corporation.

Lord Birt revealed that after 18 years, he had repaired his feud with the BBC chairman, Michael Grade.