The investigation, by a powerful committee of MPs, concluded two weeks ago – but Downing Street has refused to published it before the general election.
In the Commons, Dominic Grieve attacked the government’s failure to commit to publication on Monday – before parliament is shut down at the close of Tuesday for the 12 December election.
“We thus have a committee of parliament waiting to lay a report before this house which comments directly on what has been seen as a perceived threat to our democratic processes,” the now-independent MP warned.
“Parliament and the public ought to have, and must have, access to this report in light of the forthcoming election and it’s really unacceptable for the prime minister to sit on it and deny them that information.”
Labour’s Barry Sheerman added to the criticism of the government, asking: “Are they trying to hide something here?”
But Downing Street later confirmed the report would stay under wraps, arguing it takes about six weeks for such an intelligence report to be cleared.
Before he became prime minister, both Mr Johnson, and his predecessor Theresa May, declined to say if Russia had interfered in Brexit, arguing there was no evidence yet.
But Ms May acknowledged Russian interference in elections “in a number of countries in Europe” and the head of the Commons media committee, Damian Collins, said it was “a big and serious problem”.
The Commons intelligence and security committee then launched its probe, with the power to take evidence, in private, from the intelligence agencies.
Mr Grieve told the Commons the report had been sent to the prime minister on 17 October, the Cabinet Office having already concluded there was no classified information to prevent its release.
“That confirmation should have been received by today, to thus enable publication before the house is dissolved, but I regret to say that it has not,” he protested.
The uncertainty follows repeated criticism of Ms May’s government for failing to properly investigate “foreign influence and voter manipulation” in the Brexit vote, as the media committee called it.
Downing Street fought off calls for a “Mueller-style” inquiry, on the scale of the US probe into alleged collusion with Russia by Donald Trump’s presidential campaign.
No 10 said a “number of processes” needed to be gone through to clear a report likely to contain sensitive information.
“This usually takes several weeks to complete. The committee is well informed of this process,” a spokesperson added.
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