Simon Hughes, who gave evidence against a NoW journalist after his phone was hacked said others were afraid to join him

Senior parliamentarians declined to give evidence in court against a News of the World journalist for fear of upsetting News International, the deputy leader of the Liberal Democrats said today.

Simon Hughes, whose phone was hacked by an investigator on behalf of the NoW, told the Commons that other MPs declined to join him in the witness box in 2006 out of fear.

"I have absolutely no doubt that some people were not willing to give evidence because they were afraid," Hughes said. "They were afraid of going into the public domain to take on people working either directly or indirectly for one of our land's major newspapers."

It is understood that his remarks apply to at least one former cabinet minister. The evidence from Hughes in 2006 helped convict Glenn Mulcaire, the private investigator employed by the NoW, and its former royal editor Clive Goodman.

The warning from Hughes was echoed by Tom Watson, a Labour member of the Commons culture select committee, who said that MPs were scared of senior News International figures such as its chief executive Rebekah Brooks.

Speaking in a Commons debate, in which MPs agreed to refer the phone-hacking scandal to the powerful standards and privileges committee, Watson said: "The truth is that, in this House we are all, in our own way, scared of the Rebekah Brookses of this world.

"It is almost laughable that we sit here in parliament, the central institution of our sacred democracy – among us are some of the most powerful people in the land – yet we are scared of the power that Rebekah Brooks wields without a jot of responsibility or accountability.

"The barons of the media, with their red-topped assassins, are the biggest beasts in the modern jungle. They have no predators; they are untouchable. They laugh at the law; they sneer at parliament. They have the power to hurt us, and they do, with gusto and precision, with joy and criminality. Prime ministers quail before them, and that is how they like it. That, indeed, has become how they insist upon it, and we are powerless in the face of them. We are afraid. If we oppose this motion, it is to our shame."

John Whittingdale, Conservative chairman of the culture committee, said recent allegations about the NoW published by the New York Times, contradicted evidence given to his committee last year.

Les Hinton, the former executive chairman of News International, and Andy Coulson, the former NoW editor who is now the Downing Street director of communications, told the committee that Goodman was a rogue reporter. They said they had no knowledge of the hacking.

"Some of the information that has entered the public domain in the past few days certainly appears to contradict some of the evidence that we received," Whittingdale said. "I agree that this is an extremely serious matter, and it is not just about MPs. The illegal obtaining of information about any individual is to be deplored."

Chris Bryant, the shadow Europe minister who securedthe debate amid evidence that his phone was targeted, said the committee should examine a series of areas including:

• How many MPs were investigated by Mulcaire and did they include ministers?

• Was the hacking limited to the NoW or did it include other newspapers?

• Was MI5 notified that ministers' phoned were hacked?

• Could the Commons introduce further security measures to protect MPs' correspondence?

• Did the Metropolitan police "fully perform its duty of care towards" the Commons by contacting all MPs were on lists compiled by Mulcaire.• Have any witnesses who have already given evidence to the culture committee lied to the house? What action should be taken against them if they have lied?

• Should the law be changed to tighten provisions against hacking MPs' phones?

Bryant pleaded with the standards and privileges committee to be more aggressive with witnesses. "The House should become far more carnivorous," he said.