MI5 Director General Ken McCallum says Russia attempted to influence the 2016 Brexit referendum through Kremlin-backed media and social media troll activity. The warning follows renewed attention on the issue sparked by comments from then-Greater Manchester Mayor Andy Burnham and later debate after the UK prime minister raised the matter publicly.

While multiple outlets report McCallum confirms that such interference was attempted, he cautions against overstating its effects or “amplifying” Russian propaganda. He says there is a meaningful distinction between what may have been attempted and what actually changed, describing any influence on the referendum outcome as marginal at most and saying the Kremlin’s trolls failed to significantly sway voters.

Several sources also frame McCallum’s intervention as a response to a fresh political row over how the information is discussed. Outlets note that the dispute includes disagreements across parties about whether the revived debate reflects evidence or fuels a “propaganda victory” for Moscow by keeping Russian narratives in the headlines. The central point across reporting is confirmation of attempted interference, paired with a warning not to magnify its impact.