The widow of Alexander Litvinenko has said Boris Johnson should not have suppressed the parliamentary report on Russian interference in British politics, saying the delay helps the Kremlin and feeds suspicions of a cynical government “cover-up”.

Marina Litvinenko said the prime minister was in danger of making the same “mistake” as Theresa May, who as home secretary refused to hold a public inquiry into her husband’s murder in 2006 by polonium poisoning in central London.

“I’m very disappointed. We saw the same thing in my husband’s case,” she said, as the deadline passed for clearing the keenly awaited intelligence and security committee (ISC) report on Russia for publication before the general election.

Two Kremlin assassins poisoned Alexander Litvinenko, who was an FSB officer turned dissident, with a radioactive cup of tea. It took almost a decade before a public inquiry concluded the Russian state was responsible, in an operation “probably approved” by Vladimir Putin personally.

Facebook Twitter Pinterest Marina Litvinenko holds a copy of the 2016 inquiry report on her husband’s death. Photograph: Carl Court/Getty Images

Litvinenko said on Tuesday: “Putin’s goal is to create chaos and instability. He wants to interfere in elections in the US and Europe. The report makes recommendations to protect our system. By delaying, it looks like we are playing the same game. Putin can say we’re no different.”

She said May’s refusal to publicise the facts surroundings her husband’s state-sponsored killing emboldened Moscow. Last year, Sergei and Yulia Skripal were poisoned with novichok in Salisbury – a plot May blamed on Russia’s GRU military intelligence agency. “We have another crime,” Litvinenko pointed out.

The ISC report had been due to be published early this week and was awaiting its final clearance from Downing Street to check it contained no classified national security material.

But on Monday No 10 refused to give its approval before parliament dissolved on Tuesday, prompting the shadow foreign secretary, Emily Thornberry, to ask: “What have you got to hide?” The ISC chairman, Dominic Grieve, warned that the critical dossier may not appear until six months after the December election.

The dossier, the product of 18 months’ work which was supported by research from Britain’s spy agencies and third-party experts, examines the threat posed by Russia to the UK, including its subversion and penetration of political institutions, plus Russian killings on British soil and the danger to British allies.

Ministers have struggled to justify the withholding of the report, with Michael Gove, the chancellor of the duchy of Lancaster, saying only that the report “would be published in due course” and seeking instead to criticise Labour.

During an emergency Commons debate on Tuesday on the failure to release the report, Thornberry said the decision invited suspicion: “They realise that this report will lead to other questions about the links between Russia and Brexit and the current leadership of the Tory party, which risks derailing their election campaign.”

Thornberry said that during three “mysterious” years in Russia, Johnson’s key aide, Dominic Cummings, had “allegedly forged” relationships with prominent Russians, including Vladislav Surkov, the Kremlin’s chief ideologist, whom she described as “the power behind Vladimir Putin’s throne”.

Surkov, currently serving as Putin’s personal adviser, is credited with inventing the term “sovereign democracy” to describe Russia’s authoritarian system. The US imposed sanctions on him in 2014 after Russia’s invasion and occupation of Crimea. During the 1990s, Surkov worked for the oligarch Mikhail Khodorkovsky.

Thornberry also cited the “dubious activities” of the Conservative Friends of Russia, a pro-Kremlin parliamentary group run out of the Russian embassy by Sergey Nalobin, an alleged foreign intelligence spy, who spent five years cultivating relationships with senior Conservatives.

In response, Christopher Pincher, a Foreign Office minister, accused Thornberry of engaging in a “rundown of interesting smears and conspiracy theories” and said it was “rather rich for her to suggest that the Conservative party and this government is somehow linked to Russian disinformation, given the way her own party leadership has acted”.

Grieve warned MPs the dossier would now not be published until the committee reformed under the new government “and, in 2017, that took six months”.

In a later statement, he said he was “extremely disappointed and baffled as to why the government has not given a reason why the report cannot be published”.

“This has been a standard process, right up until the point that the prime minister – against the advice of the agencies themselves – stopped us from publishing. This must not be allowed to happen again,” Grieve said.

“We cannot have a situation in which a committee of parliament is not able to share its findings with parliament and the wider public. I expect our successors on the committee will rewrite the procedures to ensure this does not occur in future.”

Downing Street was left isolated in the Commons, with the vast majority of MPs on both sides calling for the document to be published. Keith Simpson, a Conservative ISC member, said: “This report has been cleared by the intelligence and security agencies” and “civil servants and officials saw no reason why this should not be published”.

The 50-page dossier was submitted to Downing Street on 17 October for Johnson’s approval and the committee’s expectation was that it would receive political clearance last week so it could be published on Monday.

When pressed by MPs, Pincher would not say whether Johnson had read the report, but insisted that it often took longer than 10 days for final political sign off.