A claim without published detail

The core of the story is what has not been published. Speaking on The Rest is Politics podcast in an interview released on Sunday, Burnham said he had put the question of Russian meddling in the vote directly and received a clear yes. Beyond that answer, he offered nothing on the record: no account of the form the interference took, and no description of the material behind it.

What the 2020 committee report found

Parliament's own scrutiny body had reached a different conclusion about the state of the evidence. The Intelligence and Security Committee, reporting in 2020, judged that the government of the day had never established whether Russia meddled in the 2016 referendum. Two findings from that report frame the gap:

• •The government failed to establish whether Russia interfered in the 2016 EU referendum
• •The same report found Russia had sought to influence Scotland's 2014 independence referendum, in which voters rejected independence

Moscow's response

The Russian embassy in London did not immediately respond to a request for comment. In the past, Russia has rejected any role in the Brexit vote, portraying Britain as in the grip of anti-Russian hysteria.

A break with Johnson's position

Burnham, who took over as Britain's leader in July, is the first British prime minister to say openly there was evidence of Russian interference in the referendum. Boris Johnson, who campaigned to leave the EU, had said in 2020 there was no evidence of Russian interference. The referendum itself, in which Britons voted 52%-48% to leave, triggered Britain's biggest political crisis since World War Two.

Burnham gave no further details of the evidence behind his statement in the interview, released on Sunday.