Gordon Brown was advised by civil servants against launching an inquiry into press standards, a document released by the government reveals.
A memorandum from Cabinet Secretary Sir Gus O'Donnell, written in March 2010, raised concerns over costs and possible legal challenges.
It also mentioned "questions" over the timing of Mr Brown's request - coming shortly before a general election.
But Sir Gus told the BBC the ex-prime minister had made his own decision.
Mr Brown requested the the release of the memorandum, which is labelled "restricted".
This followed revelations of phone hacking and payments to police by the News of the World, and dozens of accusations of wrongdoing by the newspaper and other News International titles.
The memorandum notes that a previous report by the Commons culture committee provided "some arguments in favour of an inquiry", including a reference to a "culture" at the News of the World that had "at best turned a blind eye to illegal activity".
But it says: "From the limited information available, it is doubtful whether this case would merit the holding of a public inquiry under the terms of the 2005 [Inquiries] Act".
The committee had looked at "essentially... a localised issue involving the actions of a small number of people within the News of the World", it says.
The document adds: "Does that really amount to a matter of 'public concern' justifying a public inquiry?"
It also says: "It is questionable whether a public inquiry would be likely to uncover more evidence than the police and the committee were able to do, bearing in mind that the events in question occurred in 2005-7."
He also advised Mr Brown that launching a probe just two months before the general election, which took place in May 2010, would "inevitably raise questions over the motivation and urgency of an inquiry".
Mr Brown told MPs on Wednesday that Sir Gus had warned him not to start an inquiry, adding that he had tried to stand up "for the public interest".
But Sir Gus has told the BBC that he had not prevented the inquiry, saying: "I advised him it is for the PM to decide."
A Cabinet Office spokesperson said: "The advice, issued in March 2010, was based on the contents of the report of the culture, media and sport select committee into press standards and other information available at the time.
"This advice was requested by the prime minister. Decisions on whether or not to hold a public inquiry, and on its scope and nature, are always the decisions of a minister."
In Wednesday's speech, Mr Brown said he had been advised against launching a probe by the civil service, the police and Home Office.
The home secretary at the time, Alan Johnson, has said Labour decided against the move because it would have looked like "low politics".
Tessa Jowell, a former Cabinet colleague of Mr Brown, said the civil service advice was "very cautious" because of the proximity of the election.
"He (Brown) was very close to an election," she told the BBC.
"When you are close to an election, and it is right this is the case, what even prime ministers can do is very limited by the proximity of the election and not getting unfair political advantage simply because you are in government."
The coalition government has now set up a judge-led inquiry into the media.
It will look at the "culture, practices, and ethics of the press".
Following public uproar at reports of journalists' behaviour, it will also investigate the "extent of unlawful or improper conduct within News International and other newspaper organisations".