MPs have been "intimidated and frightened" by the actions of tabloid newspapers including those owned by Rupert Murdoch's News International, the Leveson inquiry has heard.
Giving evidence on Tuesday, Labour MP Tom Watson said at least a dozen fellow politicians had lived with a "sense of fear" about what would appear in the papers about their personal lives or past political mistakes.
Watson, whose political career has come to be defined by his pursuit of News International over phone hacking, said that MPs from all parties had experienced "fear of ridicule and humiliation" at the hands of Britain's tabloid press.
He said that after admitting he had been scared by fear of the tabloids other MPs came forward to him.
"I got the distinct sense this was a very solitary fear that they had felt they could share with colleagues and they weren't the only ones," he said.
He told the Leveson inquiry he planned to write to all MPs to encourage them to come forward if they had similar experiences.
Watson said he believed politicians had failed to pursue the News of the World phone hacking scandal at first out of fear.
"I think they closed their minds to the potential scandal at one of the key outlets for their message," he said. "I think the were frightened."
Watson, who was a defence minister under Tony Blair, said that it mattered to ministers how they were portrayed in News International tabloids.
"There was a mystique about the News International stable, that they had unique access to Downing Street," he said.
MPs are due to debate the controversial Commons culture committee report into phone hacking this afternoon. The report accused News International executives of lying to parliament and said Murdoch was "not fit" to run an international company.
On Tuesday the Independent reported that two journalists working for The Sunday Times had arranged for Watson to be investigated be put under surveillance in the mistaken belief he was having an affair with a fellow MP.
According to the paper, while working for the News of the World in 2009 Mazher Mahmood, the "Fake Sheikh", and news editor James Mellor planned to have Watson tailed after receiving a inaccurate tip-off.