Far-right activist Tommy Robinson says he was stopped at Heathrow Airport under counter terrorism laws and had his phones seized on Saturday evening.
A Metropolitan Police spokesperson said a man in his 40s was stopped after returning to the UK from Russia via Turkey.
A man was stopped at around 17:00 GMT under the Counter Terrorism and Border Security Act 2019, they added.
The statement said: “The man was interviewed by officers and his communication devices were seized. He was subsequently released.”
Robinson, 43, posted a video on X earlier in the week showing him meeting Elon Musk’s father in Moscow.
In November, Robinson, whose real name is Stephen Yaxley-Lennon, was found not guilty of a terror offence after refusing to give police access to his phone in July 2024.
He had been stopped by officers at the Channel Tunnel in Folkestone while driving a friend’s silver Bentley to Spain.
Robinson refused to give officers the Pin to his phone during the stop, saying that the device contained confidential journalistic material.