A report on Russian interference in British politics allegedly being sat on by Downing Street includes evidence from Christopher Steele, the former head of MI6’s Russia desk whose investigation into Donald Trump’s links with Moscow sparked a US political scandal.

Steele made submissions in writing to parliament’s intelligence and security committee (ISC), it is understood. A counter-intelligence specialist, Steele spent his career tracking Russian influence operations around the world and investigated Alexander Litvinenko’s 2006 murder.

The cross-party committee has been examining Russian interference in British politics for more than a year. It took evidence from both the UK’s spy agencies and experts on Kremlin intelligence and disinformation tactics such as Steele.

Members examined claims that the Kremlin tried to distort the result of the 2016 EU referendum, starting work after the former prime minister Theresa May had warned that Russia was sowing discord by “weaponising information” in the UK.

The report was due to be published on Monday. However on Thursday, Dominic Grieve, the MP who chairs the committee, accused Boris Johnson of sitting on the report – potentially preventing its publication before the general election.

Downing Street is normally given 10 working days to clear an ISC report, to ensure it contains no classified matters, according to ISC sources – although No 10 has disputed this, saying the process typically takes six weeks.

No 10 sources said that clearance was not expected to be given on Friday, leaving only Monday and Tuesday for the document to appear before parliament dissolves. It cannot be published when the Commons does not sit, meaning if approval is withheld it will not appear before next month’s general election, which has already prompted allegations by opposition politicians of a cover-up.

Speaking in the House of Commons on Thursday, Grieve said no explanation had been given for the “apparent delay”, with the report passed to Downing Street on 17 October. Sources said Britain’s spy agencies had already signed off the report before it was passed to No 10 for final sign off.

Two sources told BuzzFeed that British intelligence found no evidence of Russian meddling in either the 2016 referendum vote or the 2017 general election. However, Steele’s involvement in the committee’s unpublished dossier raises the stakes considerably. Before going into private business intelligence, Steele spent 22 years as an MI6 officer, including four years at the British embassy in Moscow, where he watched the collapse of the Soviet Union.

In 2006 Steele led the MI6 investigation into the polonium killing of Litvinenko, a former FSB officer turned dissident. Steele swiftly concluded the Russian state was responsible. A 2015-16 public inquiry ruled that Vladimir Putin had “probably approved” the hit carried out by two Moscow assassins.

Steele’s privately commissioned dossier on Trump and Russia – leaked in January 2016 – said that the Kremlin had been cultivating the future US president for at least five years. In April the US special counsel Robert Mueller corroborated Steele’s central claim that the Russians ran a “sweeping and systematic” operation in 2016 to help Trump win.

Since then Steele’s firm Orbis has documented attempts by Russia to influence election outcomes in several European states. Unlike in Soviet times, when the Kremlin supported western communists, Moscow now uses covert and overt methods to boost populist far-right parties, including via social media.

The intelligence and security committee exists to provide cross-party oversight of the government’s security and intelligence activities. It meets weekly in secret at undisclosed locations, although its reports are made public.

The committee’s inquiry in Russian activity in the UK began in November 2017, and research was commissioned from the intelligence agencies, while submissions were sought from third-party experts.

Four months later, the novichok poisoning of Sergei and Yulia Skripal in Salisbury intensified the committee’s programme of work. Written evidence was collected by the end of June 2018, and oral hearings were held in the second half of 2018.

The committee’s annual report said that members examined allegations about “Russia’s interference in the UK’s EU referendum and the possible interference with UK political parties’ data”.

Experts who gave evidence were informed on Wednesday evening that the report was due to be published imminently. The decision to stop it from coming out is being seen inside Whitehall as unusual.