Insufficient resources were devoted to tackling threats from Vladimir Putin’s regime, the report finds

Russian interference may have had an impact on the Brexit referendum, but the effect was “unquantifiable”, according to a parliamentary report suppressed by No 10.

The report by the cross-party intelligence and security committee (ISC ) into illicit Russian activities in Britain could not say if it had affected the result of the 2016 vote.

Emily Thornberry, the shadow foreign secretary, said the disclosure raised “serious questions” about the safeguards in place for the general election next month.

“If it is correct that our security services have been unable to reach a conclusion about the extent or impact of Russian interference in the 2016 referendum, then it raises serious questions which require serious answers,” she said.

“Boris Johnson therefore needs to clear up the confusion,