Former Labour government spin doctor Alastair Campbell is giving evidence to the Leveson Inquiry into media standards.
Mr Campbell downplayed the "perceived power" of newspapers to dictate election results, but admitted there had been attempts to engage with all UK national titles in the run-up to the 1997 general election - including those owned by Rupert Murdoch.
He said he believed the Labour party did not win in that year because it was backed by Mr Murdoch, but that Mr Murdoch backed Labour because he believed it was on course to win.
The inquiry last week heard from David Cameron's former communications chief Andy Coulson, who denied any "grand conspiracy" existed between the Government and Mr Murdoch's News International, which owns The Times, The Sunday Times and The Sun.
Mr Coulson insisted he saw nothing "improper" between the press and politicians during his time in the role.
Mr Campbell , who served as director of communications for Tony Blair between 1997 and 2003 and once worked for the Daily Mirror, is expected to face questions along similar lines.
He previously appeared at the inquiry in November, when he was questioned on the general activities of the British press and described some newspaper ethics as "frankly putrid" .
Eight Cabinet ministers - including David Cameron and Culture Secretary Jeremy Hunt - were recently granted "core participant" status in the inquiry , giving them the right to see key documents in advance.
Emails highlighted during evidence from James Murdoch, former chairman of News International and Rupert Murdoch's son, led to claims Mr Hunt quietly backed the bid by News International parent company News Corp's bid to take over BSkyB, owner of Sky News.
At the weekend, Labour leader Ed Miliband renewed his call for Mr Hunt to quit over the matter.
Former cabinet secretary Lord O'Donnell, the first to give evidence at the inquiry on Monday, told the inquiry he believed David Cameron's links with the media were too close.
The peer - who retired from the key post at the end of last year - said he had tried to ensure ministers worked through the civil service and maintained a distance from the press.
But he admitted that he had not always been successful.
"I think the Prime Minister himself, the current Prime Minister, has said that he felt his relationships had got too close, and I agree with that," he said.
Mr Cameron has previously said that he and other politicians had been "too close" to media proprietors and editors, but he has stressed that his contacts were not only with News International, but with a wide range of media organisations.
Lord O'Donnell was asked about the exchanges between Adam Smith, Culture Secretary Jeremy Hunt's special adviser, and News Corporation lobbyist Fred Michel.
Mr Smith resigned last month after admitting that the contacts over the BSkyB bid had become too close. Labour has been demanding that Mr Hunt quit for allowing the situation to get out of control.
Lord O'Donnell said it was for ministers to authorise their special advisers' activities, but there was not likely to be a written record of instructions.
Monday's hearing began with News International hitting out at "fantasy" allegations made about Mr Murdoch's "sinister" back-room dealings with politicians.
Robert Jay QC, counsel for the Leveson Inquiry, was accused of "headline grabbing" by suggesting the media mogul was suffering "selective amnesia" about his discussions with Margaret Thatcher.
The idea that the pair had made an implicit pact over lunch in 1981 to allow his purchase of The Times was a "science fiction theory", according to the company's barrister Rhodri Davies QC.
"Mr Murdoch has nothing to lie about," said Mr Davies.
Sky News political editor Adam Boulton and former Press Complaints Commission chairman Lord Wakeham are due to appear at the inquiry on Tuesday, with former home secretary Jack Straw expected to take to the witness box on Wednesday.
Mr Cameron , who is expected to give evidence later in the inquiry, set it up last July in the wake of claims that the now-defunct News International title the News Of The World hacked murdered schoolgirl Milly Dowler's phone after she disappeared in 2002.