The SNP’s leader at Westminster has written to Boris Johnson demanding that he take immediate steps to allow the suppressed report into Russia’s interference in the British political system to be published.

Ian Blackford, the leader of the third-largest party in the Commons, called on the prime minister to begin appointing members of parliament’s intelligence and security committee, necessary to allow the controversial document to be released.

“It is unacceptable that your government has repeatedly and intentionally failed to take steps to establish the committee and has sought to escape scrutiny on vital issues,” Blackford writes in a letter that has been shared with the Guardian.

“The public interest and the imperative is and has always been clear: lift your sanction on publishing this report and re-establish the intelligence and security committee so that it can be immediately published,” the SNP MP added.

Facebook Twitter Pinterest Ian Blackford: ‘It is unacceptable that your government has repeatedly … sought to escape scrutiny on vital issues’. Photograph: House of Commons/PA

A report on Russia’s spying activities against the UK and its attempts to penetrate the British establishment had been prepared by the committee in the last parliament, and had been made ready to publish when the election was called.

Members of the committee saw evidence of Russian infiltration in Conservative political circles, but it is unclear how much of that concern reached the final document, which some sources say was watered down even before it went to Johnson.

Play Video 0:53 Boris Johnson says there is no evidence of Russian interference in UK elections – video

Ministers have repeatedly said there are no examples of “successful Russian interference” in the 2016 EU referendum or an election, although there is scepticism as to whether that has been properly investigated.

The report was nevertheless awaiting final clearance from Downing Street, to check it did not contain any classified information, when the election was called. No 10 said it was not possible to clear it in time, a point disputed by the previous chairman of the committee, former MP Dominic Grieve.

Downing Street eventually said after the election that the report was cleared. But its release depends on the appointment of nine cross-party backbench MPs and peers to the committee’s membership, a task that falls to Johnson after consulting with other parties.

Last time, committee members were not appointed until November 2017 – five months after the general election, prompting complaints that “effective and robust oversight of the intelligence community” had been “left in a vacuum for so many months”.

In recent years, the SNP has had one member of the committee, including at one point Blackford himself. But party sources said they had heard nothing from No 10 to suggest the appointment process had even begun.

The party acknowledges that the appointments process can take a while to find people willing to serve on the committee, which meets in secret in Westminster. But it wants Johnson to produce a timetable swiftly.

“Russian interference in elections is widespread and well documented, the evidence that Russia poses a direct threat to the functioning and operability of democracy among our allies in the EU and beyond is overwhelming,” Blackford writes.

“If this report, as you have recently claimed, shows that Russia has never interfered in any democratic event in the UK then it is inexplicable that you chose not to restore public trust and publish this report before the 2019 general election.”