British police say they stopped the far-right activist Tommy Robinson and seized his phones as he returned from a trip to Russia.

Robinson, whose real name is Stephen Yaxley-Lennon, met Elon Musk’s father in Moscow during his trip.

Russia is regarded by the UK and most western powers as a hostile state, with defence officials fearing that Vladimir Putin’s regime may stage an attack as early as 2030.

The Metropolitan police said Robinson had been stopped after getting off a flight at Heathrow airport in London from Russia via Turkey.

His phones were seized under legislation designed to stop potential threats to the UK and the Guardian understands those devices will be sent for examination.

While he was in Russia, social media accounts linked to Robinson called for protests after last Monday’s knife attack in Belfast.

The monitoring group Hope Not Hate says Robinson, 43, is the “best-known far-right extremist in Britain”.

A Met spokesperson said: “Officers stopped a man in his 40s at Heathrow airport at around 17.00 on Saturday 13 June, following his return to the UK from Russia via Turkey.

“He was stopped under the provisions of Schedule 3 of the Counter-Terrorism and Border Security Act 2019. The man was interviewed by officers and his communication devices were seized. He was subsequently released.”

A Home Office code of practice for schedule 3 of the Counter-Terrorism and Border Security Act 2019 explains it can be used by police against a person suspected of being “engaged in hostile activity … if the person is or has been concerned in the commission, preparation or instigation of a hostile act that is or may be (a) carried out for, or on behalf of, a state other than the United Kingdom, or (b) otherwise in the interests of a state other than the United Kingdom.

“It is immaterial whether a person is aware that activity in which they are or have been engaged is hostile activity, or whether a state for or on behalf of which, or in the interests of which, a hostile act is carried out has instigated, sanctioned, or is otherwise aware of, the carrying out of the act.”

On social media, Robinson portrayed himself as the victim of an overbearing state persecuting him for his political beliefs. He said he was held for about three hours, with two phones seized. He said he would need money for legal costs and asked supporters for donations.

Those who consider Putin’s Russia to be a significant threat see Robinson’s remarks about the country as concerning. Last week he told the Guardian from Moscow: “I’ve come to see how this country got itself so well on to the straight and narrow and see the beauty of a civilised society here.”

Robinson added: “Russia is not the enemy of Britain. That narrative has long since died a natural death. There are those who benefit from pushing Russia as an enemy but everyone laughs at those people now.”

The Royal United Services Institute, a London-based thinktank, said: “Russia is one of the most prolific actors when it comes to conducting hybrid campaigns to influence the politics of other countries, including the UK. These campaigns blend online influence, cyber-attacks and other measures to try to cause offline effects – and events such as the Belfast attack certainly have the kind of incendiary potential that Moscow may seek to harness.”

A rally led by Robinson attracted 150,000 people to march through London last September, and another saw 60,000 people gather in May this year.