The senior officer who investigated a suspected leak in a documentary about a Troubles massacre was not “exercised” by the film, a tribunal probing allegations of unlawful spying on journalists has heard.

The Investigatory Powers Tribunal (IPT) in London is examining claims that investigative reporters in Northern Ireland were subject to unlawful covert intelligence by the police.

Barry McCaffrey and Trevor Birney were arrested in 2018 as part of an investigation into the alleged leaking of a confidential document that appeared in No Stone Unturned, about the 1994 UVF massacre in Loughinisland, Co Down.

The two men and the company behind the documentary were later awarded £875,000 in damages after the High Court in Belfast ruled that warrants secured by police to raid their homes and business offices in the city were wrongly obtained.

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

Three police forces – the Police Service of Northern Ireland, Durham Constabulary and the Metropolitan Police – are now part of a three-day IPT hearing about alleged unlawful covert surveillance.

On Tuesday, former Durham detective Darren Ellis, who took a leading role in the investigation, began giving evidence at the Royal Courts of Justice.

Ben Jaffey KC, for Mr McCaffrey and Mr Birney, suggested Mr Ellis was “exercised” about the contents of the documentary.

“It contained secret information. That’s my only observation,” Mr Ellis replied.

He later continued: “Nothing exercised me. You keep using that word … I’m a professional individual.”

The former officer also told the tribunal: “My concern about No Stone Unturned was that it contained secret documents, that’s it.”

Mr Jaffey later claimed that Mr Ellis thought the documentary should not have been aired.

But Mr Ellis said: “I don’t think it should have contained secret documents … All I ask people to do is stick to the law.

“With respect to the guys, if there is criminality, there’s criminality, if there isn’t, there isn’t, it’s not personal.”

Mr Jaffey later suggested that Mr Ellis tried to persuade the Law Society of Northern Ireland, which regulates solicitors, to “take action” against Mr Birney and Mr McCaffrey’s lawyers.

However, the former Durham police officer said he did not ask the body to intervene.

Mr Ellis told the tribunal: “I was not asking the Law Society to do anything but I was concerned.”

He continued: “I was investigating the documents … I can’t investigate with my eyes closed.

“I explained to the right people what my concerns were. It wasn’t done with any ill intent, it was done to bring it to their attention.”

The hearing before Lord Justice Singh, Lady Carmichael and senior barrister Stephen Shaw KC is due to conclude later this week with a judgment expected in writing at a later date.