Rebekah Brooks told how her "complicated" relationship with ex lover Andy Coulson came under strain as they chased David Beckham stories for rival papers.
Brooks used her friendship with Victoria Beckham and her footballer husband to demonstrate the "Chinese Wall" between them as they edited sister papers, the Sun and the News of the World.
Brooks began editing the Sun in 2003 while co-defendant Coulson took over from her at the News of the World, the Old Bailey heard.
Giving evidence for a fourth day, Brooks, 45, told how she had lunch with Mrs Beckham as the stories about her husband's alleged affair were afoot.
She told the Old Bailey trial: "The two papers were rivals and pretty strong rivals. I think Andy and I had been very good at keeping the Chinese Wall.
"It was a hostage to fortune discussing what we were working on. He was on the weekly, I was on the daily with more opportunity to publish.
"Beckham is a good example. So Andy would have known that I knew the Beckhams a little socially, we are not close friends but would see them occasionally for dinner. I was also trying to get Victoria or David to do things for the paper.
"He would know I had direct access to them so if he is working on a story and there is something afoot as the paper was working on the fact David Beckham was allegedly having an affair with a woman, to even mention that to me could be fatal to his paper.
"He would not know the day he mentioned it I had lunch with Victoria.
"So he may say on Thursday 'we will have the Beckham story this weekend' and I may respond 'sorry we are doing it tomorrow'. It was too complicated. Things were difficult, it was strained for a while."
Brooks, of Churchill, Oxfordshire, denies conspiring to hack phones, conspiring to commit misconduct in public office and conspiring to cover up evidence to pervert the course of justice. All seven defendants deny the charges against them.
Brooks said discussing stories with Coulson had become "difficult" and "caused unnecessary angst to an already complicated situation".
She told the court the Daily Mirror and Daily Mail had "stolen a march" on the Sun after the News of the World ran spoof editions when it published an exclusive on Beckham's alleged affair.
"Obviously I was not best pleased about that situation," she said.
Brooks said that in 2004 she had a "strong professional relationship" with then-home secretary David Blunkett after the pair worked together on Sarah's Law.
They would have dinner and attended the Police Bravery Awards together, she said.
Asked by her lawyer Jonathan Laidlaw QC whether she knew Blunkett's voicemails had been hacked in 2004, Brooks replied: "Absolutely not."
She told the court Coulson contacted her the night before the News of the World published a story on Blunkett's alleged affair with a woman.
The woman had not been named in the News of the World but the Sun ran an exclusive story the next day naming her as Kimberly Quinn, the court heard.
Brooks said: "I think from memory I had told Andy and the News of the World we have got this… and we had gone full steam ahead with the full name."
She told the court the Sun had found newspaper cuttings of Blunkett and Quinn and she confirmed this with a special adviser to the politician.
Speaking about the alleged affair, Brooks said: "We had no evidence. Like the rest of Fleet Street, all we had was in the News of the World.
"The Home Secretary's office had not denied it. One clue must have been in their statement, which was 'We are not commenting', which in newspaper-speak is not denying.
"It was inevitable her name was going to come out."
Brooks told the court "things were much better" between her and Coulson when they exchanged a series of late-night texts shortly before he travelled to Sheffield to meet Blunkett in August 2004.
"My guess is they (the texts) would have been pretty personal," she said.
She told the court she did not believe Coulson told her that he was going to meet Blunkett.
"If he said to me 'I'm going to see David Blunkett', I would have been intrigued," she said.
Brooks went on to discuss a business lunch she had with the then wife of golfer Colin Montgomerie in 2005.
Eimear Cook, who was married to the Scots-born former Ryder Cup captain for 14 years, had earlier in the trial given evidence claiming that Brooks had spoken about how easy it was to hack phones if the factory setting was not changed.
However, Brooks' recollection was about Cook declaring she was a victim of violence, and the hacking comment "was not the kind of thing I would say".
Retelling a conversation about the couple's troubles and how it was being seen in the press, Brooks said: "She felt Colin Montgomerie was being seen as the white knight in this and she was getting criticised.
"She said he had been violent towards her and I was very surprised. She was a complete stranger to me. She obviously wanted to tell me that."
This prompted an approach by Brooks for her to speak out in the Sun as part of a campaign to toughen up the law on domestic violence, which she declined.