Johnson was speaking ahead of the publication on Thursday of the first part of an extensive judge-led inquiry into British press standards which could result in tougher regulation of the industry.
The former journalist told BBC radio in Delhi on Sunday that he would strongly oppose any moves by his Conservative party leader, Prime Minister David Cameron, to introduce statutory regulation of the press if the Leveson Inquiry recommends it.
“I am a bit nervous we are heading in the opposite direction to many other countries in the world which are liberating their press and allowing free speech, and I think statutory regulation is not something that I would support,” Johnson said.
“What are the attractions to London as an international investor? What makes it a great place to live? It’s because you have a stable system where it is very largely uncorrupt.
“I can tell you that compared with most other jurisdictions in the world, we have a political system that is largely free of financial corruption and bribery.
“I think it is very largely because we have a pretty uninhibited, vociferous and exuberant media that gets on and turns over all sorts of flat rocks.
“If you go around sterilising, pasteurising and homogenising the media you will have a bad effect on our democracy.”
Foreign Secretary William Hague said he was a “big supporter of press freedom” but stressed that he wanted to read the report by senior judge Brian Leveson before giving his verdict on it.
He rejected suggestions that Cameron had already made up his mind to reject state regulation, pointing out that “none of us” had yet seen Leveson’s recommendations.
But the leader of the main opposition Labour party, Ed Miliband, urged Cameron to show confidence in the inquiry’s findings and agree a rapid timetable for its implementation providing its findings are reasonable and proportionate.
Writing in Monday’s Guardian newspaper, Miliband said: “Parliament set up this inquiry with the power to examine all the evidence and reach conclusions. We need to show confidence in this process, not try and invent a new one.”
Cameron set up the inquiry in response to revelations that the Rupert Murdoch-owned News of the World tabloid had hired a private investigator to hack the phone of murdered schoolgirl Milly Dowler.
Over eight months of hearings, it has heard evidence from victims of phone hacking and press harassment, editors, journalists and politicians.