The UK government "actively avoided" examining whether Russia tried to influence the outcome of the Brexit referendum, a report into Moscow's activities has said.
The heavily-redacted report by Parliament's Intelligence and Security Committee (ISC) said the government "took its eye off the ball" and failed to respond to the threat posed by Russia.
It noted the widespread allegations that Russia sought to influence voters in the 2016 Brexit referendum but concluded it would be "difficult - if not impossible" to assess whether any such attempts had been successful.
ISC member and SNP MP Stuart Hosie said the government "actively avoided" trying to address the questions over Russia's reported attempt to influence the Brexit vote.
He said no one in government wanted to touch the issue of Russian interference with a "10-foot pole".
Hosie said that no-one in government knew if Russia interfered or sought to influence the 2016 referendum "because they did not want to know".
He said: "There has been no assessment of Russian interference in the EU referendum and this goes back to nobody wanting to touch the issue with a 10-foot pole.
"This is in stark contrast to the US response to reported interference in the 2016 presidential election.
"There should have been an assessment of Russian interference in the EU referendum and there must now be one, and the public must be told the results of that assessment."
The committee said the government was "was slow to recognise the existence of the threat" from Russia.
It said the intelligence agencies and ministers should have been aware of the risk of Russian interference as a result of "credible open source commentary suggesting that Russia undertook influence campaigns in relation to the Scottish independence referendum" in 2014.
Publication of the committee's report was postponed by prime minister Boris Johnson's decision to call a general election and the subsequent delays in setting up the ISC in the new parliament.
Committee member and Labour MP Kevan Jones said there was "no reason" for the delay in the publication of the report.
He said claims by the prime minister it required six weeks to get his confirmation for the report were "categorically not true".
He also said that claims by Number 10 the report needed to be further circulated for comment in government were "not true".
Jones said the ISC report was sent to the prime minister on 17 October.
He said Johnson's confirmation for its release was received the day after the general election in December, having taken "record time".
Labour MP Lisa Nandy said it was "extraordinary" that the report was not published before last December's general election.
The committee said Russian influence in the UK is "the new normal" as successive governments have welcomed oligarchs with open arms.
There were Russians with "very close links" to its leader Vladimir Putin who were "well integrated into the UK business, political and social scene - in 'Londongrad' in particular", it said.
The report warned of the threat posed by Putin-linked business elites in the UK.
The ISC noted that "a number of members of the House of Lords have business interests linked to Russia, or work directly for major Russian companies" and these relationships should be "carefully scrutinised" given the potential for Moscow to exploit them.
The committee said: "It has been clear for some time that Russia under Putin has moved from potential partner to established threat, fundamentally unwilling to adhere to international law - the murder of Alexander Litvinenko in 2006 and the annexation of Crimea in 2014 were stark indicators of this.
"We therefore question whether the government took its eye off the ball because of its focus on counter-terrorism: it was the opinion of the committee that until recently the government had badly underestimated the response required to the Russian threat - and is still playing catch-up."
Foreign secretary Dominic Raab said: "We've been clear that Russia must desist from its attacks on the UK and our allies.
"We will be resolute in defending our country, our democracy and our values from such hostile state activity."
In a 20-page response to the report, the government rejected the accusation it had "badly underestimated" the threat from Russia.
It said: "The government has long recognised there is an enduring and significant threat posed by Russia to the UK and its allies, including conventional military capabilities, disinformation, illicit finance, influence operations, and cyber-attacks.
"As such, Russia remains a top national security priority for the Government."
The government also rejected the call for an assessment of alleged Russian activity during the Brexit referendum.
It said: "We have seen no evidence of successful interference in the EU Referendum.
"Where new information emerges, the government will always consider the most appropriate use of any intelligence it develops or receives, including whether it is appropriate to make this public.
"Given this long standing approach, a retrospective assessment of the EU Referendum is not necessary."