The Chief Constable of a scandal-hit police force has apologised to three journalists - including two from the Press Association - for using anti-terror legislation to spy on their phones.

Cleveland Police used controversial Regulation of Investigatory Powers Act (RIPA) authorisations to track calls and texts made by reporters after critical stories were published in July 2013 about a senior civilian officer's resignation.

At the time the Independent Police Complaints Commission said it was "completely unacceptable" for Ann Hall, the assistant chief officer, to quit ahead of a disciplinary hearing for alleged misconduct.

The Press Association covered the story and it has since emerged that Cleveland Police monitored the phone of Tom Wilkinson, a Newcastle-based reporter, and his colleague Owen Humphreys, a photographer with the national news agency.

Cleveland Police has also admitted spying on the phone of Northern Echo reporter Graeme Hetherington after the story about Ms Hall broke.

The force already apologised to Mr Hetherington and his colleague Julia Breen in January for monitoring their phones in 2012 in a bid to unearth their sources following other critical stories about Cleveland Police conduct.

The force said it monitored Mr Wilkinson's phone usage over four days, not listening in on the content of calls or texts, but recording the numbers used in and out.

Chief Constable Iain Spittal said: "Following a ruling by the Investigatory Powers Tribunal earlier this year that in 2012 Cleveland Police had, in a small number of instances, used Regulation of Investigatory Powers Act (RIPA) authorisations unlawfully the force launched a review of all such authorisations dating back to that time.

"As part of this ongoing work we've found three additional instances of RIPA being used on journalists, two from PA and one from the Northern Echo, in 2013 in what was a disproportionate manner.

"When such evidence is found we will, as we have here, contact those affected and give them full details.

"We will also, as we have here, offer our full apologies."

Mr Wilkinson said he had covered many stories about Cleveland Police in his 16 years with the Press Association, including the news conference in January where the force announced it was scrapping its Professional Standards Department in the light of its unlawful use of RIPA.

"In some ways I am not surprised that the force monitored my phone," the 44-year-old said.

"But it was still unpleasant to find out, almost four years after the fact, that they have used anti-terror laws to snoop on me, merely for doing my job."

In December, the Investigatory Powers Tribunal in London heard that the force was motivated to find the source of damaging leaks.

A series of damaging stories over the years have led to calls from James Wharton, Tory MP for Stockton South, for the force to be disbanded if it does not make improvements.