Police and MI5 subjected a former BBC journalist to a “long and consistent campaign of unlawful interference” by obtaining communications data from his mobile phone, a tribunal has heard.

The surveillance was targeted at Vincent Kearney, who was the BBC’s Northern Ireland home affairs correspondent, and occurred over an eight-year period as authorities sought to identify his sources.

Details of the monitoring by MI5 and police forces in Northern Ireland and England have been revealed in a case the BBC and Kearney have brought before the investigatory powers tribunal (IPT), a special court that investigates complaints against the UK’s spy agencies.

MI5 admitted last year that it had unlawfully obtained Kearney’s phone data on two occasions between 2006 and 2009. However, in court on Wednesday it emerged the intrusion by several police forces and the Security Service was more intrusive and wide-ranging.

The IPT heard that the Police Service Northern Ireland (PSNI) and the Metropolitan police also accepted that they unlawfully obtained Kearney’s communications data, violating his rights under the European convention on human rights.

In one operation, the tribunal heard, PSNI obtained information relating to 1,580 calls or texts the journalist made or received. His lawyers said there was evidence to suggest police had at one stage obtained “geographic data” based on his phone records.

The admissions by the police and MI5 “reveal repeated and consistent illegality on the part of multiple public authorities over a period of many years”, said Jude Bunting KC, a lawyer representing the BBC and Kearney, in written submissions to the tribunal. “The sheer volume and extent of interferences with journalistic material in this case is unprecedented,” he added.

Kearney, now the northern editor at the Irish broadcaster RTÉ, was a familiar face on BBC Northern Ireland where he worked until 2019. He covered politics and security for the broadcaster, and worked on high-profile stories about the police.

In submissions to the IPT, his lawyers argued the communications data obtained by police across several operations between 2009 and 2014. The data, they said, would enable the forces to “see who [he] was interacting with, where, and when”. Communications data does not include the content of calls or messages.

The IPT also heard how the PSNI had created a “detailed intelligence profile” of Kearney containing details about his journalism and private life. This included information about his family members and who he lived with.

After MI5 admitted last year that some of its actions were unlawful, the agency disclosed additional information about how it had obtained Kearney’s communications data on an undefined number of occasions in 2006. Its officer had also made an internal request to “open a file” concerning the journalist.

A lawyer for MI5 told the tribunal said “we entirely accept” that applications to obtain Kearney’s data were not lawful, but said the agency’s actions did not amount to a “long and sustained campaign”.

In a statement to the tribunal, Kearney said the admissions by MI5 and the police forces “reveal a systematic and years-long pattern of accessing my journalistic sources”. He added: “I am not aware of any other journalist in the UK or Ireland who has been targeted in such a sustained way over so many years.”

Kearney’s lawyers have argued the intrusion has had a “measurable chilling effect” on his ability to operate as a journalist, and had “damaged and, in some cases, destroyed” his relationships with sources. “His colleagues in the BBC have also suffered damage to their source relationships,” they said.

A spokesperson for the BBC said: “What happened in this instance was wrong and must never be repeated. The independence of what we do is hard won and it’s something that we will fight to protect.”

Kearney is seeking damages from the PSNI. The force has argued that compensation is not appropriate in this case. Its lawyers said efforts to obtain the journalist’s data had been “reasonable” and intended to “further criminal investigations”.

A spokesperson for the Home Office said the case “covers historic activity” and legislation governing the acquisition of communications data had been updated to include enhanced protections for journalists and journalistic material.