The Murdochs' appearance before MPs for a grilling about the phone-hacking scandal was brought to a dramatic halt after an activist attempted to hit Rupert Murdoch in the face with a paper plate covered in shaving foam.

Murdoch's wife Wendi Deng, who was sitting behind her husband at the culture, media and sport committee hearing, leapt up to defend her husband and appeared to hit out at the attacker as security guards and police rushed across the room to apprehend him.

The attack happened just before 5pm on Tuesday and the News Corp chairman and chief executive was back answering MPs' questions within 20 minutes, having removed his foam-spattered suit jacket.

Murdoch's assailant, who was sitting four rows back in the committee meeting room at Portcullis House near the Houses of Parliament, apparently identified himself on Twitter shortly before the attack as a standup comic and UK Uncut activist called Jonnie Marbles.

Marbles appears to have tweeted moments before he invaded the hearing. "It is a far better thing that I do now than I have ever done before #splat," he wrote on the social media network.

Moments after the committee chairman, John Whittingdale MP, suspended the meeting, a man wearing a checked shirt was seen outside the meeting room at the House of Commons in handcuffs.

Cries of "no, no," could be heard as the man ran towards Rupert Murdoch, who was sitting in front of MPs on the committee alongside his son James.

"He was sitting four rows back," said Guardian journalist Jane Martinson, who was among the reporters in the room when the attack took place. "He walked calmly to the front and smacked it in Rupert's face."

Marbles had earlier tweeted: "I'm actually in this committee and can confirm: Murdoch is Mr Burns."

He added: "Rupert Murdoch appears to be going senile." He also tweeted: "It might be quicker if Baby Murdoch simply listed all of the things that he does know.

"One gets the sense that they haven't really done the required reading ahead of their presentation. Think they may fail this module."

Marbles describes himself on his Twitter page as an "activist, comedian, father figure and all-round nonsense. Tweeting in an impersonal capacity."

But UK Uncut moved swiftly to distance itself from the invader. "The pie in Murdoch's face was NOT a UK Uncut action, everyone!" it tweeted soon after.

Martinson added: "The man lobbed a plate of shaving foam into Murdoch's face at point-blank range. There was an astonishing reaction from Wendi, who, sitting behind her husband, immediately returned fire.

"James looked stunned, several members of room gasped, but Wendi then sat on the desk calmly wiping foam from her husband's face. There was foam all over her blue-painted toes as well as two police officers who immediately grabbed him. There was shock that he got the foam in given the tight security. Another man with a long beard was also questioned."

She added: "All the press were kept in an overspill room as the committee resumed. I'm not sure how the foam man hid the paper plate. He was wearing black combat trousers and walked straight past me from the back row where the public was sitting to within inches of Murdoch.

"Wendi was on her feet lobbing the plate back at her husband's assailant before James got up. Another woman - small and dark-haired - was the one who accosted the assailant first."

Labour MP Tom Watson, one of the members of the select committee, told Murdoch: "Your wife has a very good left hook."

Louise Mensch, a Conservative MP and fellow select committee member, said Murdoch had shown "huge guts" in being willing to carry on.

Another Labour MP, Chris Bryant, described the attack as "just despicable". He said witnesses should not be treated in such a manner and described it as contempt of parliament.

Associates of Marbles said he "lives and breathes politics" and had been involved in previous UK Uncut protests.

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