What did the prime minister say, and why could it be significant?

The Russia topic came up as part of a wide-ranging interview Burnham gave to The Rest is Politics, excerpts of which were released on Sunday, in which he appeared to suggest he had been given new information about the Brexit vote.

“I asked the question coming to Downing Street: ‘Was there interference in the 2016 referendum from Russia?’ And I’ve had the clear answer that yes, there was,” he said.

The prime minister did not say whom he had asked, or set out in detail what the answer was. But his comments suggest he had been given new information of some kind, though he then switched to talking about Russian disinformation in general.

“These things are important now to put clearly on the record, and I believe, help voters in Germany and France understand that some of this politics is instigated via our enemies, namely Russia,” he said.

“And, I think we’ve been too much on the back foot on that, actually. And we haven’t informed people sufficiently about the extent to which people are seeking to disrupt the political process from overseas.”

What could Burnham have been told?

It is hard to decipher from what the prime minister has said so far.

A possibility is that he was given a summary of a recent assessment by the UK’s intelligence agencies, in effect a formal conclusion by them. Another is that it was a relatively informal conversation with officials, where opinions were simply exchanged.

The difference is significant – if there was a fresh assessment it would run counter to the previous position, established under a succession of Conservative governments in the aftermath of the Brexit vote.

What was the conclusion of previous inquiries?

There were no serious official investigations into Russian interference attempts in 2016, not least because the Conservatives had no appetite to order them. As time passed, it became increasingly difficult to do so.

The topic was addressed by parliament’s cross-party intelligence and security committee in its Russia report, published in July 2020, which took evidence in secret from the UK’s intelligence agencies before publishing a partly redacted report.

It concluded that the government “had not seen or sought evidence of successful interference in UK democratic processes”. No formal post-referendum assessment had been made, the committee added, and more generally the UK intelligence community was accused of taking its “eye off the ball” when it came to the Russian threat.

What could have happened in 2016?

This is an old controversy with three main aspects. First that a “troll army” of state-linked Russian accounts tweeted about the referendum in the run-up to the vote, though estimates of numbers have varied wildly from 54 to 150,000 (many of which were deleted).

Second that Russian English-language media outlets RT and Sputnik published a large amount of anti-EU and pro-Brexit content, which had a wide reach. The digital campaign group 89up said the two broadcasters had published 261 articles that achieved 134m potential page impressions.

The third aspect, and the most contentious, were claims that Arron Banks, a donor to the pro-Brexit campaigner Nigel Farage, had links to Russia. Leaked emails showed he met Alexander Yakovenko, then the Russian ambassador to the UK, three times – a figure he later revised up to four – and that he was offered the chance to participate in a goldmining deal in Russia.

A subsequent investigation by the National Crime Agency into £8m-worth of loans Banks provided to Brexit campaigns run by Farage concluded the money was legitimately his and there was no evidence of wrongdoing.

But the EU referendum was also a complex, closely fought campaign in which many points of view were in play. The idea that one country, with an interest in weakening the UK and the EU, could have had a decisive influence in a vote of 33.5 million people is debatable.

What’s going on then?

The prime minister is making a broader argument that Britain needs to reconsider its relationship with the EU, arguing Brexit has not delivered what was promised. Highlighting that there could have been Russian efforts to interfere with the vote raises questions about the outcome, though Downing Street insisted on Monday it regarded the result as legitimate.

Burnham is due to make a Commons statement on Monday afternoon on Brexit and Europe, where he will also have the opportunity to say if the intelligence agencies have made a fresh assessment about whether there was Kremlin interference in 2016. If he fails to do so, he risks being accused of exaggeration.