Thurlbeck admitted that without the “Nazi theme” allegation, which Mosley denied, there was no public interest defence in printing the story.
He also claimed that if Beckham, who brands himself as a family man, had cheated on Victoria then the public had a right to know.
Mosley, 71, was splashed over the front page of the now-defunct News of the World in March 2008, under the headline “Formula 1 boss has sick Nazi orgy with 5 hookers”.
He was awarded a record £60,000 in privacy damages over the story. It later emerged that that the News of the World reporter behind the article instructed a prostitute to ensure she secretly video Mosley making a Nazi salute.
“The Nazi allegation was completely untrue and, to me, enormously damaging. I was outraged by it,” Mosley said.
“However long I live now, that is the number one thing people think of when they hear my name. It really matters.”
Thurlback said that Rebecca Loos, who sold a kiss and tell story about Beckham to the New of the World, made a six-figure sum for the revelations. He said there was “huge public interest” in publishing the story.
“[Beckham] was sponsored left, right and centre,” Thurlback said. “He was always promoting himself with his family as a happy modern man. It was a wholesome image that the family cultivated and the public bought into on a massive scale, and we exposed that as a sham.”
Thurlbeck was fired by News International in September after being arrested in April on suspicion of hacking phones while working at the now-defunct Sunday tabloid. At today’s Leveson Inquiry hearing, he said he would not comment on phone hacking.