Two investigative journalists have called for answers ahead of a tribunal hearing to examine allegations that they were subject to covert surveillance by UK authorities.

Senior legal figures sitting on the Investigatory Powers Tribunal are hearing a case brought by Northern Ireland-based film-makers Barry McCaffrey and Trevor Birney.

In 2018, Mr McCaffrey and Mr Birney rose to public prominence after they were controversially arrested as part of a police investigation into the alleged leaking of a confidential document that appeared in a documentary the men made on a Troubles massacre.

The Police Service of Northern Ireland (PSNI), citing a conflict of interest, asked Durham Police to lead the investigation into the inclusion of the Police Ombudsman for Northern Ireland document in the No Stone Unturned film on the 1994 UVF massacre in Loughinisland, Co Down.

Former PSNI chief constable Simon Byrne later unreservedly apologised for how the men had been treated and the PSNI agreed to pay £875,000 in damages to the journalists and the film company behind the documentary.

The 2020 settlement came after a court ruled that the warrants used by police to search the journalists’ homes and Fine Point Films had been “inappropriate”.

In 2019, Mr Birney and Mr McCaffrey lodged a complaint with the Investigatory Powers Tribunal asking it to establish whether there had been any unlawful surveillance of them.

The respondents in the case are the PSNI, Durham Police, MI5, the Security Service Government Communications Headquarters (GCHQ) and several Government ministers.

In a two-day hearing at the Royal Courts of Justice in London, the tribunal will also probe a separate issue, pre-dating the documentary, which involves claims that police officers unlawfully accessed Mr McCaffrey’s phone records.

Mr McCaffrey had been investigating alleged police corruption around the time his data was said to have been accessed by the PSNI in 2013.

Mr Birney and Mr McCaffrey were greeted by supporters as they arrived at court on Wednesday morning accompanied by their solicitors, Niall Murphy and John Finucane.

“We’re here simply to seek the truth,” Mr Birney told reporters outside the Royal Courts of Justice.

“We’re here to find out exactly what was going on in the years leading up to our arrest in 2018. We don’t know what we’re going to hear this morning. We don’t know how this is going to go.

“We don’t know if the PSNI and Durham (Constabulary) are going to come clean and tell us what actions they were taking against journalists in Belfast over the last 10 years.”

Mr McCaffrey said: “We feel that we need to know, and journalists and society need to know, if police have been surveilling journalists for no other reason than we’re doing our job.

“Journalism isn’t a crime. Journalists shouldn’t be treated as criminals or as criminal suspects, and if that is the case, UK police have an awful lot to answer for.

“And we need answers today. We need the courts and the police to tell us exactly what they’ve done. Society needs to know that journalists aren’t being targeted by police.”

Lord Justice Singh, Lady Carmichael and senior barrister Stephen Shaw KC are sitting on the tribunal for the hearing.