Former News of the World investigations editor Mazher Mahmood admitted today that he once "foolishly" changed electronic records to cover up a mistake in his reporting.
Mahmood, also known as the 'fake sheikh' after a string of undercover stories gained through that disguise, resigned from the Sunday Times in 1989 after executives discovered he had tampered with a file in the newspaper's computer room, the Leveson Inquiry into press standards heard.
He told the hearing: "I acknowledge it was wrong. I was young, I was naive, it was a foolish thing to do, I acknowledge that."
The incident arose from a complaint about a story Mahmood wrote saying a police chief inspector had been demoted to constable following a conviction for drink-driving when he had only been reduced to the rank of inspector, the inquiry heard.
Roy Greenslade, then the Sunday Times's managing editor (news), said in a witness statement that the reporter claimed the mistake came from material supplied by a local news agency in Devon.
The agency showed that its original story was correct, but the paper's computer records contained a version of the submitted copy with the mistake in it.
The Sunday Times's news editor, Michael Williams, learned that Mahmood had recently visited the paper's computer room, which was "off limits" to editorial staff, the inquiry heard.
Greenslade, who is now a media commentator and professor of journalism at City University, said he and Williams suspected the journalist had tampered with the file, although he denied this when questioned.
Senior Sunday Times executives agreed that Mahmood should be fired, but when they emerged from their meeting they learned he had already resigned, the hearing was told.
Mahmood, who was 24 at the time, told the inquiry: "I was a young reporter, and I had had a series of run-ins with Greenslade while at the paper. I made a mistake...
"Rather than incur the wrath of an executive I didn't get on with, I foolishly thought the best way would be to cover my mistake. It was the wrong thing to do, and I resigned."
Mahmood also denied he had bribed a colleague to change his copy, an accusation made by former Sunday Times news editor Michael Williams in the British Journalism Review.
Asked to justify using a witness for stories who had been found to be unreliable in court, Mahmoud said that he had "had front-page splashes from crack addicts".
He added that one crack addict had stolen his voice recorder.
Also at the Leveson inquiry on Wednesday, murder victim Joanna Yeates's former landlord accused police of leaking information about him to journalists following his arrest on suspicion of her murder.
Retired school teacher Christopher Jefferies made the accusation in a statement released by his solicitor, read out at the inquiry, and called for an independent inquiry.
The statement, released by Stokoe Partnership, said: "It has become apparent that evidence put before the Leveson Inquiry confirms our earliest concerns about the confidentially with which the arrest and detention of our client was dealt with by those investigating the murder of Joanna Yeates.
"As a result of our attendance at the police station and of our reviewing of the material in the media, it became apparent that information had been deliberately leaked by as yet unidentified individuals in flagrant breach of their duty.
"Our client strongly believes this to be the case, as there was information within the public domain which was only known to those privy to the investigation material.
"Our client is of the view that this information had been leaked and we share that view."
Jefferies was responding to evidence - disputed by Avon and Somerset Police - that Daily Mirror editor Richard Wallace gave the Leveson Inquiry into media standards last week.
Wallace apologised to Jefferies and told the inquiry that his judgment was affected by off-the-record briefings from the force in which they appeared confident that Jefferies "was their man".
Colin Port, the Chief Constable of Avon and Somerset Police, denied the claims made by Wallace and said the force was "actively challenging" his comments.
Last year Jefferies accepted a libel payout from eight national newspapers, including the Daily Mirror, over false allegations they made against him following the murder of his tenant. He had previously told the Leveson Inquiry that the national press "shamelessly vilified" him.