Rebekah Brooks told the wife of a professional golfer how easy it was to hack the phones of famous people, the Old Bailey was told today.

Eimear Cook said that Mrs Brooks had warned her of the ease with which voicemails could be eavesdropped over lunch at the house of mutual friends.

Mrs Cook, who married Colin Montgomerie, told the phone hacking trial: “She told me it was ludicrous people weren’t aware of the simple way people could protect their voicemail.”

She explained that friends had suggested she meet Mrs Brooks, then Rebekah Wade, because she might be able to give an inside view on the media at a time she was under intense media pressure as a result of her separation from Mr Montgomerie.

Mrs Brooks, she said, had arrived “flustered” at the home of the wealthy Manoukians in Knightsbridge, but soon became “gossipy” and referred to phone hacking.

Mrs Cook said: “She said that it was so easy to do and she couldn’t believe all those famous people who have all these advisors and they don’t know they need to personalise their PIN codes to make their voicemails secure.”

Mrs Cook, who has three daughters by Mr Montgomerie, told the court she thought the lunch had taken place in September or October 2004.

However, Jonathan Laidlaw QC, for Mrs Brooks, showed her a copy of Mrs Brooks’s office diary which suggested that the lunch had been on 20 September 2005 – a year later than she had testified. Mrs Cook said that she must have made a mistake with the dates.

Reminding Mrs Cook that she was on oath, Mr Laidlaw also suggested she had wrongly referred to Mrs Brooks recalling an incident of domestic abuse because a well-known incident involving Mrs Brooks had taken place six weeks after the lunch.

He challenged the witness: “You have, I suggest, lied to the jury.”

Mrs Cook replied: “I categorically deny that…. There’s nothing calculating about the evidence I have given. I’m here because the police have asked me.”

She added: “I have not made anything up…. I’ve no reason to lie.”

Earlier the police head that Mrs Brooks had arranged a low-key meeting with Andy Coulson, a week before he resigned as Communications Director to David Cameron. In January 2011, Mrs Brooks emailed her two personal assistants: “Need to see Andy at 7.30am in Victoria – somewhere discreet like a hotel. Not the Goring.”

Her electronic diary later suggested the meeting had taken place on 14 January 2011, seven days before Mr Coulson’s resignation on 21 January. The court heard that on 21 January, Mrs Brooks’s personal assistant, Cheryl Carter, had emailed her: “Please call Andy Coulson.”

Mrs Brooks, Mr Coulson and two others deny plotting to hack phones. All defendants in the case have also pleaded not guilty. The trial continues.