The editor of the News of the World at the time murdered Walton schoolgirl Milly Dowler's phone was hacked in 2002 said she had believed her paper had tried to respect the family's privacy.

Rebekah Brooks, who was arrested on suspicion of phone hacking on Sunday shortly after standing down as chief executive of News International, said today that the practice was "pretty abhorrent".

She said: "Of course I have regrets. The idea that Milly Dowler's phone was accessed or authorised by the News of the World is abhorrent to me.

"It is with ultimate regret the speed of the investigation has been too slow."

Questioned by MPs, she said: "It may sound quite frankly ridiculous now, but at the time in 2003, I believed with both the Milly Dowler case and the Soham case the press had exercised great caution and tried to respect the privacy of the families.

"Clearly the allegations came out two weeks ago and if they are true they are appalling and contradict this statement (in 2003).

"My instant reaction was shock and disgust that a family that had already suffered so much - this allegation clearly added to that suffering.

"I immediately wrote to Mr and Mrs Dowler to say we would get to the bottom of the investigation."

She said the first time she heard allegations Milly's phone was hacked was two weeks ago from the media.

She said: "My instant reaction like everybody else was one of shock and disgust."

Ms Brooks said the first thing she did was write to the Dowler family apologising.

They met the Dowler family lawyer and then wrote to Surrey Police asking for more information, she said.

She said the idea of a News of the World employee had hacked Milly's phone was "staggering".

Earlier her former boss Rupert Murdoch was hit by a foam pie by a member of the public.

Almost instantly his wife, Wendi Deng, threw a punch at the man, who was removed from the chamber in handcuffs.

Brian Cathcart, a Kingston University journalism professor and part of the Hacked Off campaign was in the chamber.

In a series of tweets he said: "So, we all come this far so that someone can push a plate of foam in Murdoch’s face."

“Came from somewhere behind me and all happened in slow motion.

“Walked around and pulled his paper plate and foam out of a blue plastic bag.”

“For this, Nick Davies [Guardian journalist] does all that work."

After being foam pied, Mr Murdoch read a statement saying: "Behaviour that occurred went against everything I stand for. It not only betrayed the readers and me, but thousands of people."

He also said: "Invading people’s voicemails is wrong.

"Saying sorry is not enough and must be put right."

He finished by saying: "This country has given me and our companies and employees many opportunities. I hope my contribution to Britain will one day be recognised."

The Dowler family met Mr Murdoch last week to hear his apology and told him to clean up his newspapers.

Bob, Sally and their daughter Gemma had believed that Milly was alive after learning her voicemails had been listened to and deleted.