British Prime Minister Andy Burnham has said that Russia interfered in the 2016 Brexit referendum, using the claim to caution voters in France and Germany about Moscow-backed attempts to shape their own politics, Reuters reported.

Burnham, who became prime minister in July, is the first British leader to state publicly that there was evidence of Russian meddling in the vote held a decade ago. Speaking on The Rest Is Politics podcast, released on Sunday, he said that when he arrived at Downing Street he asked whether Russia had interfered in the referendum and was given a clear answer that it had.

He did not explain how he believed Russia had interfered or what evidence his statement was based on. The Russian embassy in London did not immediately respond to a request for comment. Moscow has previously denied any involvement in the Brexit vote and has accused Britain of anti-Russian hysteria.

A Break From Johnson

Burnham’s remarks mark a clear shift from the position of former Prime Minister Boris Johnson, who campaigned for Britain to leave the EU and said in 2020 that there was no evidence of Russian interference in the referendum.

That same year, a report by parliament’s Intelligence and Security Committee found that the British government had failed to determine whether Russia meddled in the 2016 vote. The report also concluded that Russia had tried to influence Scotland’s 2014 independence referendum, in which voters chose to remain part of the UK.

Britons voted by 52% to 48% to leave the EU in 2016, a result that triggered the country’s deepest political crisis since World War II.

A Warning To European Voters

Burnham said voters in European democracies need to be better informed about efforts to disrupt their political systems. He argued it was important to put the issue clearly on the record, saying it could help people in Germany and France understand that some of the politics they see is being stirred up by Britain’s enemies, namely Russia.

The comments come as Burnham reopens Britain’s long-running debate over its relationship with Europe. Last month, he said Britain could consider rejoining the EU in the future and that he could campaign to take the country back into the bloc at the next general election.