The arrest of former News International chief executive Rebekah Brooks was "quite a surprise", her spokesman has said.
The 43-year-old was held on suspicion of phone hacking and corruption after keeping an appointment at an unnamed London police station. She remains in custody.
Her spokesman said on Sunday: "She had been told as early as a week ago that she wasn't on the radar, then suddenly on Friday there was a request to meet.
"She attended today and it was quite a surprise to her on her arrival to be arrested. She was going, anticipating to help with their inquiry. She wasn't anticipating that she was going to be arrested."
Ms Brooks's arrest cast doubt on whether she would be able to appear before the Culture, Media and Sport Committee on Tuesday with Rupert Murdoch and his son James. It was unclear to what extent she would be able to answer questions if she did appear.
Her spokesman said: "It has many implications for Tuesday. Over the next 24 to 36 hours her lawyers will have discussions with the select committee to see if it will still be appropriate (to attend). She certainly wants to."
The former Sun and News of the World editor resigned as News International chief executive on Friday to avoid distracting attention from the company's efforts to "fix the problems of the past".
She had devoted more than half her life to serving the British arm of Rupert Murdoch's News Corporation empire. He regarded her highly and was still standing by her last weekend.
After arriving in the UK to handle the crisis, he was asked what his priority was. "This one," he replied, gesturing at her and smiling.
She is the 10th person to be arrested since Scotland Yard's fresh investigation into phone hacking was launched in January.