Prior to being made Tony Blair's communications director Alastair Campbell was political editor at the Daily MirrorCredit: Matthew Fearn/PA
Speaking at the Leveson inquiry, Campbell, a former political editor at the Mirror, said that he had been briefed on invoices showing that the title had "paid a private investigator for looking at me, Peter Mandelson at certain points, and a member of my family".
He says in his written statement to the inquiry that the private investigator was Jonathan Rees, who has been shown to have carried out investigative work for both the Daily and Sunday Mirror and the News of the World.
"I do not know the stories he was pursuing, so cannot judge either whether a 'normal' journalist would have been unable properly to investigate, or whether a public interest defence could be mounted with regard to the inquiries being made," Campbell said.
Asked by the inquiry counsel whether he had any direct experience of phone hacking, Campbell confirmed that he had been contacted by the Metropolitan police's hacking investigation, Operation Weeting, to inform him that details about him and his partner had been found among the notes of private investigator Glenn Mulcaire.
He said he has also been contacted by officers from Operation Tuleta – the Met's computer hacking investigation, which made its first arrest last week – and briefed on computer hacking.
He told the court: "I am not remotely putting myself in the category of some of the people that have been here but yes, I have had experience of phone hacking and some of these other dubious practices."
Campbell also alleged that he had been threatened by senior journalists at News International after speaking out about the phone-hacking scandal.
In his witness statement, the former spin doctor described going on television in the wake of the Guardian's July 2009 hacking story and saying that the story "was not going away, that David Cameron should reconsider his appointment of Andy Coulson, and that what appeared to be emerging was evidence of systematic criminal activity on a near industrial basis at the News of the World".
He told the inquiry that following his TV appearances he received "a series of what can only be termed mildly threatening test and phone messages from senior journalists and executives and News International".
Campbell added that the Labour MP Tom Watson, who has played a significant part in the political investigation into phone hacking in recent years, was "on the receiving end of a similar and more robust approach".
Campbell, himself a former tabloid journalist who was political editor of the Daily Mirror in the 1980s, said it was "possible to see a similar if more muted approach" in the coverage of the inquiry, which he accused of "questioning the judge and the panel" and forming the "beginnings of what is likely to become a sustained campaign to undermine it unless it comes up with conclusions that the press finds palatable".
Following yesterday's evidence from former News of the World deputy features editor Paul McMullan, who said it was "blatant and obvious" that editors at the tabloid knew about phone hacking, Campbell added to the speculation over Andy Coulson's denial that he was aware of the practice during his time there.
Coulson, who was editor from 2002 to 2006 and went on to become David Cameron's director of communications, has consistently denied any knowledge of phone hacking.
But Campbell said that the amount of money being paid to private investigators cast doubt on Coulson's denial.
"When the whole Andy Coulson thing was at its height ... they wouldn't necessarily know everything that everyone did in the pursuit of a story but they would certainly know that more and more money was being spent on private investigators.
"Now would they not stop and ask why are we spending all this money on PIs?
"Probably not, because they knew."
Campbell also challenged the editor of the Daily Mail, Paul Dacre, on his assertion before a House of Lords select committee that the Mail titles have never obtained a story through phone hacking.
Referring to the 2006 Operation What price privacy now? report, which showed that the Daily Mail had made more requests to investigator Steve Whittamore than any other title, Campbell said Dacre "ought to be able to answer for every single transaction".
"If he can't do that then he can't substantiate that statement to a House of Lords committee."
A draft of Campbell's written statement was leaked online on Sunday by the blogger Paul Staines, who publishes political blog Order-Order under the pseudonym Guido Fawkes.
Fawkes removed the document on Tuesday after being issued with a section 19 order under the inquiries act 2005, and has been summoned to appear before the inquiry tomorrow to explain the leak.
Trinity Mirror, publisher of the Daily and Sunday Mirror, declined to comment on Campbell's testimony.