Police mounted a covert surveillance operation following the arrest of two journalists in a bid to unmask one of their sources, a tribunal has heard.

The Investigatory Powers Tribunal was told that the arrest of film makers Barry McCaffrey and Trevor Birney in 2018 was a “disruptive” tactic to see if the reporters would reach out to the source after their release from custody.

The tribunal is examining allegations that the award-winning journalists were subject to unlawful covert surveillance by UK authorities.

It heard a series of new revelations as the case opened on Wednesday, including allegations that the Met Police illegally obtained Mr McCaffrey’s phone data in 2011 – data that police in Northern Ireland subsequently secured seven years later as part of another probe into the reporter’s work.

In 2018, Northern Ireland-based Mr McCaffrey and Mr Birney were controversially arrested as part of a police investigation into the alleged leaking of a confidential document that appeared in a documentary they 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.

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

The 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 (IPT) asking it to establish whether there had been any unlawful surveillance of them.

The tribunal case began in London on Wednesday and was due to sit for two days but the hearing was adjourned before lunch on the opening day due to the late disclosure of police documents.

One of those documents was a directed surveillance authorisation approved by former PSNI chief constable George Hamilton.

This gave the green light for covert surveillance of an individual whom officers suspected of being the source of the leaked document from the Police Ombudsman’s office.

Prior to adjourning the case, tribunal chair Lord Justice Singh invited counsel for the journalists to outline their cases in broad terms.

Ben Jaffey KC, representing Mr McCaffrey, said the directed surveillance authorisation document, which he got first sight of at 7.30am on Wednesday, was key to the case.

“The nature of the operation is now pretty clear,” he said.

“It was to arrest the two journalists with the intention of releasing them the same day – the intention was not to ask any serious questions or because they needed to be interrogated under arrest. But because they wanted to create what is sometimes euphemistically called a disruption or a surprise.

“They would then be released at the end of the day and then aggressive covert attempts would be made to see if they got in contact with their source.

“The whole purpose of the operation was to unmask the journalistic source.”

The surveillance operation was conducted for two weeks before Mr Hamilton granted an application for it to be cancelled.

Mr Jaffey set out a series of grounds challenging the legality of the surveillance authorisation. He disputed a police contention that the operation was not intrusive.

He said a reference to obtaining recorded audio indicated the strategy was to be intrusive.

The senior counsel said surveillance of that nature required approval of a judicial commission, not solely a chief constable.

Mr Jaffey said the authorisation application was done at the request of the senior investigating officer, Darren Ellis of Durham Police.

He claimed the document contradicted Mr Ellis’s statement to the tribunal in which he said he was unsure whether a directed surveillance authorisation was progressed in the case.

During the hearing, Mr Jaffey also questioned the legal basis for a police request to Apple for an emergency preservation order on Fine Point Films’ iCloud account following the arrest of the journalists.

The tribunal also heard that as part of the 2018 investigation, police “reinterrogated” phone data it requested from the Metropolitan Police in London related to Mr McCaffrey.

It emerged that the Met Police obtained Mr McCaffrey’s data in 2011 in another investigation aimed at revealing the identity of a source.

Mr Jaffey said he and his client were only made aware of this revelation last Friday.

“We had no idea that communication data had been obtained in that operation,” he said.

The lawyer added: “It seems overwhelmingly likely that that communications data authorisation was unlawful.”

He claimed the PSNI’s subsequent move to source the data secured from the Met for the 2018 investigation was also unlawful.

The tribunal was already set to probe claims that the PSNI itself unlawfully accessed Mr McCaffrey’s phone records in 2013 as part of an unrelated investigation into his journalistic work.

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

Mr Jaffey said the PSNI had acknowledged that its actions in that case had been unlawful and the only matter for the tribunal to determine was the remedy.

“What happened there is that there was no prior authorisation and there was no attempt to apply the correct legal test,” he said.

The police forces represented at the hearing will respond to the applicants’ case when the substantive hearing resumes.

Earlier Mr Jaffey criticised the late disclosure of police documents.

“This case is I’m afraid a shambles which is not ready for considered judicial determination at the moment,” he said.

Mr Birney’s counsel Stephen Toal KC also expressed concern at the late disclosure.

“This is not the approach that is taken in Northern Ireland to matters of discovery and disclosure,” he said. “It is a shambles and it certainly is not indicative of how we usually do cases there.”

Lord Justice Singh, who was sitting on the tribunal panel alongside Lady Carmichael and senior barrister Stephen Shaw KC, told all legal parties in the case to agree “rigorous directions” to ensure the case could resume again without undue delay.

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

Outside court, Mr Birney and Mr McCaffrey expressed shock at the details that had emerged on the first day.

“I think it was stunning just to hear our counsel outlining just what has been going on since 2011,” Mr Birney told reporters outside the Royal Courts of Justice in London.

“It is still somewhat shocking.”

Mr McCaffrey said: “It’s shocking, but there’s still much more that we need to know – we still need answers.”

He added: “Three different police forces in the UK have been trawling journalists, every journalist in the UK should tonight be asking themselves was I one as well. Was it me?

“And they should be going to the IPT and asking and finding out have they been victims like Trevor and myself.”