Top lawmakers in both houses of parliament are raising concern over the timing of the now-completed government study's release.
Johnson's Conservatives are keen to avoid any suggestion that Britain's divorce from the European Union was triggered unfairly.
The pro-Brexit campaign defied most pollsters to win by a 52 to 48 percent margin - an outcome that left the country deeply split.
Senior cabinet minister Michael Gove said the 50-page dossier compiled by the intelligence and security committee was "going through the appropriate procedure".
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"It will be published in due course," Gove told BBC radio.
But he refused to say whether it would be published before the December 12 snap general election, which could decide when or even if Brexit will go ahead.
Johnson's minority government could be voted out of office if it fails to win an all-out majority.
The main opposition Labour Party is ready to let Britons vote again on whether to leave the EU if it regains power for the first time since 2010.
And some of the smaller opposition parties simply want Brexit stopped.
Intelligence and security committee chairman Dominic Grieve - an independent who quit the Conservatives over Brexit -- called the government's apparent foot dragging "jaw dropping".
Upper House of Lords member Donald Anderson, also an independent, warned that the "unjustified delay undermines" the committee's work.
"It invites suspicion of the government and its motives," Anderson said Monday.
"What's the prime minister got to hide?" Labour House of Lords member Dianne Hayter asked.
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The Guardian newspaper said Tuesday that the dossier "has already been approved by the intelligence agencies themselves" in a process that began in March.
It also reported that a part of the government's analysis is based on information provided by former MI6 foreign intelligence officer Christopher Steele.
The so-called Steele Dossier figured prominently in the initial stages of the scandal surrounding what US intelligence agencies determined was Russian interference in US President Donald Trump's 2016 election.
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