A free press has meant the freedom to "spread lies and half-truths", Jeremy Corbyn has claimed.
The Labour leader hit out at the "billionaires" who "own the bulk of the British press" in a speech to his party's annual conference in Liverpool.
Mr Corbyn said the free press in the UK had granted journalists the freedom to "smear the powerless, not take on the powerful".
But he also vowed to "protect the freedom of the press to challenge unaccountable power" as he spoke of journalists killed for doing their job.
He said: "It turns out that the billionaires who apparently own the bulk of the British press don't like us one little bit.
"Now it could be because we're going to clamp down on tax dodging. Or maybe because we don't fawn over them at white tie dinners and cocktail parties.
"Or it could even be because Tom Watson has been campaigning for the second part of the Leveson media inquiry to be set up - something the last Prime Minister promised, but failed to deliver.
"We must, and we will, protect the freedom of the press to challenge unaccountable power.
"Journalists from Turkey to Myanmar and Colombia are being imprisoned, harassed or sometimes killed by authoritarian governments and powerful corporate interests just for doing their job of trying to found out the truth of the oppression that happens in their societies."
Mr Corbyn continued: "But here, a free press has far too often meant the freedom to spread lies and half-truths, and to smear the powerless, not take on the powerful.
"You challenge their propaganda of privilege by using the mass media of the 21st century: social media.
"And we'll do it in traditional ways too. On the doorsteps, in the town centres, at the school gates, in the community centres, so that people know there is a Labour Party that will stand up for them and is ready to rebuild and transform Britain."