A journalist has launched legal action against the police after they secretly labelled him a leftwing extremist who could disrupt the Labour party conference.

Police refused to give Michael Segalov security clearance to attend last year’s Labour conference.

Legal papers disclose that police drew on confidential intelligence files to allege that Segalov had demonstrated an increased willingness to take part in protests that involved breaking the law – a claim he rejects.

The papers also show that police conceded they did not have any information to show that he had committed any criminal acts. The 24-year-old has never been arrested.

Segalov, who has written opinion columns for the Guardian and other outlets, appears on television commenting on politics and works as an editor for a cultural magazine, Huck. He has attended many Labour events, both as a journalist and a member of the party. He has interviewed senior politicians including the Labour leader, Jeremy Corbyn.

He said: “This is an important case to determine how the press can operate freely. To be labelled an extremist for carrying out my work as a journalist is incredibly distressing”.

Last September, police refused to approve his application to be an accredited reporter at the Labour party conference in Brighton, saying he had not passed the security checks that are required for the media.

Segalov says that this hindered him from doing his job as a journalist, which included interviewing politicians and researching stories – a claim denied by the police. 

At the time, police refused to explain why he had been turned down. However they have been compelled to disclose their reasons after he filed a legal claim at the high court alleging that the refusal was unlawful. A hearing is due to be held on Wednesday.

In their defence, police claimed that intelligence “established that Segalov was a known extreme activist who had taken part in demonstrations in relation to a wide range of issues.”

According to police, this intelligence suggested that while he was not involved in criminality, Segalov was increasingly willing to engage in direct action.

They claimed there was a risk that Segalov – whom they call a “known extreme leftwing (XLW) activist” – “might get involved in actions that would disrupt the conference”.

Police added that Segalov had met activists who had released cockroaches in a Byron burger restaurant before an anti-deportation protest in 2016, and then publicised the incident afterwards.

Segalov says this was the normal action of a journalist who received a tip-off and reported the protest for his magazine and provided information about it to the Guardian and other media.

A Sussex police sergeant said he had had dealings with Segalov since 2013. He claimed that while he was not suggesting that Segalov had directly committed any criminal acts, he was aware that he “had been involved in a number of demonstrations/events which had involved damage to property and/or criminal acts committed by others”.

The sergeant alleged Segalov was willing to motivate others to carry out forms of that which had sometimes been criminal and had directed anarchists to disrupt shops during a student protest in Brighton in 2015 – allegations denied by Segalov.

The sergeant also alleged that Segalov had “expressed his satisfaction” at the damage caused to Sussex University during a protest in 2013 – another claim denied by the journalist.

Segalov, who was a leftwing campaigner as a student, won an apology and £20,000 from Sussex University, which admitted it had falsely accused him of criminal behaviour during that protest.

At the hearing scheduled for Wednesday, his lawyers are seeking to persuade the high court to allow his case against Sussex and Greater Manchester police to go ahead.

Police said they were contesting the case and could not comment while it continued.