Journalists have launched a court fight after complaining about the way police identified ''confidential'' sources.
Judges today began analysing the dispute between reporters who worked for The Sun newspaper and the Metropolitan Police at a trial in London.
Evidence is being analysed by the Investigatory Powers Tribunal - which considers complaints about the way public authorities use covert techniques - at a hearing due to end on Tuesday.
Lawyers representing journalists have complained about the way police used the Regulation of Investigatory Powers Act (Ripa).
The litigation is centred on police inquiries after Conservative MP Andrew Mitchell was accused of being rude to police in Downing Street.
Complaints that the then Government chief whip had been abusive first emerged in The Sun in September 2012.
The affair became known as ''Plebgate''.
Journalists' lawyers say a central issue is whether detectives' ''recourse'' to ''the disputed Ripa powers'' in order to identify ''confidential sources'' was necessary.
Judges have been told that News Group Newspapers - which publishes The Sun - plus Tom Newton Dunn, Anthony France and Craig Woodhouse have taken action against the Metropolitan Police.
Police deny wrongdoing and say complaints should be dismissed.