Former Sun editor tells phone-hacking trial she hesitated over high cost of story, which was later published by Daily Telegraph

Rebekah Brooks has declared her "embarrassment" at not paying a public official for the MPs' expenses story when she was editor of the Sun at the Old Bailey hacking trial.

She has also admitted sanctioning payment for a story about Saddam Hussein threatening to swamp Britain with anthrax poison in 1998, refusing requests by M15 and M16 not to run the story.

During her sixth day in the witness box at the phone-hacking trial on Friday, Brooks told the jury that her failure to buy the disk with unredacted details of MPs' expense claims was one of the greatest mistakes of her career.

"In terms of errors of judgment, it's probably quite high on my list," she told the court, telling jurors how her procrastination had led to her being scooped by the Daily Telegraph in May 2009 when she was editor of the Sun, shortly before being promoted to News International chief executive.

"My news team came to me to say they had heard the unredacted information to do with the MPs' expenses fraud could be available but it was going to cost quite a lot of money.

"It was something I had to consider carefully," she said. "I thought about for too long ... I drove my news team crazy with my indecision."

She added: "I remember when the CPS [Crown Prosecution Service], they did not go to prosecute because of the high level of public interest, it was quite embarrassing that we didn't get it [the story]."

Brooks also told the jury on Thursday that there were half a dozen occasions that she could recall where she signed off on payments to public officials.

On Friday the court heard of one example when, in 1998, someone who was "clearly" a public official phoned the Sun to say the "secret service were covering up a plot by Saddam Hussein to bring in anthrax to this country".

Brooks told how in trying to corroborate the story, the security services were alerted to the Sun's investigation and she was summoned to Downing Street.

"I remember representatives from MI5, MI6, GCHQ, Downing Street and lawyers who may have been representing some of the parties," she said. "First of all by its very nature, it [the meeting] confirmed what the public official was telling us was true."

Brooks, who was deputy editor of the Sun at the time, was in charge of the paper as the editor was away, the told the court. She was asked not to proceed with the story but decided it was in the public interest and went ahead splashing with story "Saddam anthrax in our duty frees".

The source was identified after an internal inquiry as a chief petty officer and he was subsequently prosecuted.

Brooks was being questioned by her defence counsel, Jonathan Laidlaw QC, in relation to a charge that she conspired to cause misconduct in public office by sanctioning payments of £38,000 to public officials between 2004 and 2012.

The payments have been linked to one source, Bettina Jordan-Barber, a Ministry of Defence official, and did not relate to the Westminster MPs story or the Hussein story, which was published in 1998.

Brooks denies knowing Jordan-Barber or that she was a public official, but introduced examples in her career where she would have considered paying public officials as a way of explaining to the jury that if she had known the MoD official was the source, she would have to consider the public interest test for publication.

She was charged after police found 11 emails from a Sun reporter requesting her approval for payment for stories from Jordan-Barber, who he described as his "number one military contact" or his "ace military contact".

On several occasions, Brooks told jurors, she was not in the office when stories based on information provided by Jordan-Barber were published. On one occasion Brooks was in Russia or Italy, where News Corp had a lot of business interests.

On another occasion, her diary showed the story in question appeared after the News International summer party on 17 June 2009.

"Charlie and I had got married the week before and we could not go on honeymoon because of the board meeting in town that week," Brooks said.

The day after the News International party, she received an email from a Sun reporter requesting her authorisation for payments to his "top military contact".

"Great do last night by the way, met lots of people," he wrote before requesting approval for £4,000 payment for a story.

The jury was also shown an email discussing the "cover-up" of the killing of Brazilian electrician Jean Charles de Menezes in the wake of the 7/7 bombings in 2005.

One email showed that the Sun's police source believed that the former home secretary Charles Clarke was the source of a leak to the News of the World about the cover-up of the killing at Stockwell tube station.

The jury saw an email from a Sun reporter telling her his source had said: "Dick says the leak on Stockwell cover-up came from Charles Clarke."

He explained that he had requested £500 "for info on an exclusive we had last week about Kate Moss drug dealer being quizzed". He also needed the "money to smooth along" another story.

"I'm not sure it's wise putting this kind of thing down on email where this is a permanent record," he added.

Brooks was asked by Laidlaw what this could have meant. She replied that it could have be read as meaning that the reporter "did not want to put information about his sources on email" or, she said, "if you want to see something more sinister in it you could have read he did not want this payment to be discussed on email".

She added: "It could be he should not be putting the name of the source of the Stockwell cover-up on an email."

Brooks told jurors that the reporter was "very senior" and that the tone of the last line in the email was "a bit chippy". She said: "It could have been that he did not want to be questioned on the cash for one of his many sources."

Brooks also told the jury on Friday that she could not take her honeymoon in 2009 because of a News Corp board meeting in London that she was required to attend.

The jury was sent home at lunchtime on Friday after they were told by the judge that Brooks had found her six days in the witness box "tiring".

The trial continues.