British newspapers will and should be subject to some form of new external regulation, the outgoing prime minister, Tony Blair, said yesterday in a broadside that attacked the media for behaving like feral beasts and eschewing balance or proportion.

In a sweeping critique of the industry, Mr Blair claimed newspapers, locked into an increasingly bitter sales war in a 24-hour news environment, indulged in "impact journalism" in which truth and balance had become secondary to the desire for stories to boost sales and be taken up by other media outlets.

He admitted that his own attempts to bypass traditional media through websites and press conferences had been "to no avail". He also conceded that he was partly to blame for the predicament, saying his determination to convey the Labour message in the period of opposition and early years in government had made him complicit in the decline in news standards.

But he said the fierce competition for stories had led to the media now hunting in a pack. "In these modes it is like a feral beast, just tearing people and reputations to bits, but no one dares miss out."

He added that distinctions between comment and news had become so blurred that it was rare to find newspapers reporting precisely what a politician was saying. It was incredibly frustrating, he said, adding that politicians had to act immediately to rebut false charges before they became fact.

Mr Blair said he was describing "something few people in public life will say, but most know is absolutely true: a vast aspect of our jobs today - outside of the really major decisions, as big as anything else - is coping with the media, its sheer scale, weight and constant hyperactivity. At points, it literally overwhelms."

The damage that can be done "saps the country's confidence and self-belief", he said. "It undermines its assessment of itself, its institutions and above all, it reduces our capacity to take the right decisions, in the right spirit for our future."

The consequence was a fall in morale in the public services, a loss of trust between politicians and media and even a climate of fear in which those in public life dare not attack the media's sensationalist culture for fear for the media's counterblast.

In a world of 24-hour news and huge diversity of outlets, he said, it is impact that gives a competitive edge. "Of course the accuracy of a story counts. But it is secondary to impact. It is this necessary devotion to impact that is unravelling standards, driving them down, making the diversity of the media not the strength it should be but an impulsion towards sensation above all else."

"News is rarely news unless it generates heat as much as or more than light. Second, attacking motive is far more potent than attacking judgement. It is not enough for someone to make an error. It has to be venal. Conspiratorial."

Moving on to the regulation of newspapers, Mr Blair said changes were inevitable: "As the technology blurs the distinction between papers and television, it becomes increasingly irrational to have different systems of accountability based on technology that no longer can be differentiated in the old way."

He also questioned whether papers needed some system of accountability that went beyond sales. He said: "The reality is that the viewers or readers have no objective yardstick to measure what they are being told. In every other walk of life in our society that exercises power, there are external forms of accountability, not least through the media itself.

The prime minister's aides admitted he had thought long and hard before making the speech, but felt free to do so now that he was, in his own words, leaving office "still standing". Ministers conceded privately that the regulatory structure of newspapers may change over the next decade, but did not believe it would lead to direct regulation. "It is possible we could end up with a kitemark that websites pass certain tests, but it is a long way away," said one minister.

There is also ministerial and industry scepticism that EU legislation and the convergence of newspapers and broadcasting would see a single regulatory structure for newspapers and TV.

The coming EU legislation is likely to make the broadcast regulator, Ofcom, responsible for regulating the internet, but is likely to leave unregulated the content of newspapers on the website.

Audio: Michael White on Blair v the media