MPs are calling for a full review into how Cleveland Police officers used surveillance powers designed to investigate serious crime to seize journalists' call records as it tried to track down a media leak.

The force admitted its use of the Regulation of Investigatory Powers Act (RIPA) to access phone data from two Northern Echo journalists, two serving officers and a solicitor, was unlawful on four occasions.

But it denied that accessing four months' worth of records from the same people was unlawful, as it said it suspected an officer was leaking sensitive information to The Northern Echo.

Following a complaint from the two former police officers, specialist court the Investigatory Powers Tribunal indicated this week that it would find the force acted unlawfully, when it delivers its judgement in the New Year.

Labour's Anna Turley, MP for Redcar, called the allegations "shocking" and added: "These powers are granted only for the investigation of serious crimes and must always be used sensitively so that people’s privacy is not compromised. Having a free press in this country is a vital part of our democracy. We do not live in a police state.

“If the Tribunal finds the force acted unlawfully, which they are indicating will be the case, then there needs to be a full review into how this happened and to ensure oversight over the use of these powers is more rigorous so that it will not happen again.”

Alex Cunningham, MP for Stockton North, added: "As a former newspaper and radio journalist, I know how precious the protections that exist for the media are and for a police force to stand up in court and admit it misused security powers to spy on its own police officers, lawyers and a newspaper's offices and reporters beggars belief.

"Journalists, whilst they must also work within the law, should not feel shackled in any way in their investigative work through fear of their sources being compromised and it's to the Northern Echo's credit that they have covered this matter in the way they have.

"The extent of the misuse of powers was stunning and for the force to examine months of calls must have cost a fortune in police time and taxpayers money. The senior officers heading up the work and those advising them must be held accountable. I would hope that the new Chief Constable will take a very specific look at that whilst finding out exactly this misuse of powers happened in the first place and instigate training across the force to ensure there can be no repeat."

And James Wharton, Tory MP for Stockton South, said: “On the face of it this was a complete misuse of very strong powers the police have to be used in exceptional circumstances. They have used them to try to crush people.

“They (Cleveland Police) need to be completely transparent, to stop fighting every criticism that comes to them and significantly change the culture at the force. That would include, you would expect, seeing people leaving the force who were responsible for some of these activities.

Cleveland Police and Crime Commissioner Barry Coppinger said: “The protection of civil liberties is fundamental in a democratic society and all organisations, including the police, must respect that principle and the laws that exist to ensure that protection.

“I have followed the reports from this hearing. It would appear the Judges have been highly critical of Cleveland Police and have indicated they will find against the force.

“That raises serious questions about what has gone on and clearly action must be taken to establish how this has happened and to ensure there is no repeat. I will make further comment after full judgement has been delivered.”

The force accessed the phone records of former officer Mark Dias, the then Cleveland Police Federation chairman Steve Matthews, and Northern Echo reporters Julia Breen and Graeme Hetherington. A mistake by the force on one of the RIPA forms also showed that a number attributed to former Echo reporter Chris Webber actually belonged to a Daily Mirror journalist.

The scale of the surveillance - more than a million minutes - was said to be 35-times the size of that used in the “Plebgate” scandal that saw the Metropolitan Police use RIPA to access the records of three Sun journalists.

After the hearing, Mr Matthews' barrister Hugh Tomlinson QC, said: "This displays an astonishingly careless attitude towards RIPA laws. These are supposed to be incredibly draconian laws that are only used in the most extreme circumstances."