The European Court of Human Rights said on Thursday it had asked the UK government to answer questions about alleged Russian interference in elections after a legal challenge.
The UK parliament's Intelligence and Security Committee (ISC) in 2020 said it could not come to firm conclusions about any Russian meddling, including in the 2016 Brexit vote or the referendum on Scottish independence two years earlier.
But the report said the government under prime minister Boris Johnson "took its eye off the ball", and critics pointed to his Conservative party's links to wealthy Russian donors as one explanation for official inaction against Moscow.
The ECHR's response follows a claim lodged by a cross-party group of three MPs after the High Court in London rejected the case in 2021.
They claim the failure of the government to investigate "credible allegations" of interference in the electoral system breaches its obligations under the European Convention on Human Rights that protects the right to free and fair elections.
In a letter to the MPs, the ECHR has accepted the claim through the first stage of the court's process and says it now requires the UK government to respond to five questions by the end of April.
The trio -- Ben Bradshaw, of the Labour party, Caroline Lucas, of the Green Party and Alyn Smith of the Scottish National Party (SNP) -- were part of a group of six who lost a bid to bring a High Court challenge in June 2021 against Johnson over his alleged "failure" to probe possible Russian interference in UK elections.
Democracy campaign group The Citizens, which has worked with the MPs on the case, has contrasted the UK response to the United States, where multiple investigations have concluded Russia did try to influence the 2016 presidential election.
The case was about protecting the "integrity of our politics", not reversing Brexit, Bradshaw said in a statement on Thursday.
"A number of us have been warning about (Russian President Vladimir) Putin's real intent for more than 10 years.
"We know that his long-term strategy has been to destabilise and divide Western democracies."