The independent police watchdog launched an investigation on Friday into claims that a senior officer passed information to Rupert Murdoch's News International during a probe into phone hacking at one of its newspapers.
The inquiry is examining whether details passed by the unnamed officer to an executive at News International, the British newspaper arm of Murdoch's News Corp, during the police's 2006 investigation constituted a criminal offence or misconduct.
London's Metropolitan Police (MPS) launched that investigation when senior royal aides reported their suspicions that voicemails on their mobile phones had been illegally accessed by journalists from the News of the World Sunday tabloid.
The investigation led to the conviction of the paper's royal reporter and a private detective.
News International claimed the practice was limited to that rogue reporter but last year admitted phone hacking had been widespread, causing a scandal that shook Murdoch's empire and rocked the press, police and political establishment.
The officer who headed the original inquiry told lawmakers last July that News International chiefs had deliberately hindered their investigation.
Police are now carrying out three new criminal investigations and it was information from one of these that led to the Independent Police Complaints Commission (IPCC) probe into the senior officer.
The allegation of an inappropriate disclosure of information from an MPS officer to an executive at News International raises important issues of public confidence in the MPS, IPCC Deputy Chair Deborah Glass said in a statement.
I believe it is right that we independently investigate this to determine if there was any wrongdoing.
The MPS said after careful consideration it had decided not to suspend the officer, who is based within the Specialist Operations unit which handles counter-terrorism and royal protection and which handled the original hacking inquiry.
It said the information which prompted the investigation had been passed to detectives by the Management and Standards Committee set up by Murdoch which is trawling through 300 million emails to hunt for any evidence of criminality.
Information it has uncovered has led to the arrest of some of the most senior journalists on Britain's top-selling Sun tabloid newspaper as well as a number of serving and former police officers over claims they were paid for passing information to reporters.
(Editing by Janet Lawrence)