The police chief in charge of the phone hacking investigation has spoken of her anger as a detective in her own team was arrested over leaks to journalists.
Officers arrested and suspended their 51-year-old colleague as former News of the World feature writer Dan Evans was questioned on suspicion of voicemail interceptions.
Deputy Assistant Commissioner Sue Akers expressed annoyance over the detective constable's alleged "unauthorised disclosure" during the investigation.
The Operation Weeting chief said: "I made very clear when I took on this investigation the need for operational and information security. It is hugely disappointing that this may not have been adhered to."
The detective constable was arrested at work on Thursday afternoon before being released on bail until September 29.
Mr Evans, 35, was bailed after facing several hours of questioning on suspicion of conspiring to unlawfully intercept voicemails, sources said.
The journalist, who was arrested by appointment at a London police station, was suspended by the axed Sunday tabloid after interior designer Kelly Hoppen, who is stepmother to actress Sienna Miller, brought a damages claim alleging that he tried to hack into her voicemails in June 2009.
The former paper and lawyers for the journalist have said an extensive investigation found no evidence to support Ms Hoppen's claims. It is thought that Scotland Yard arrested the writer over separate phone hacking allegations.
Mr Evans, who joined the News of the World in 2005 and has been suspended since April 2010, is the 14th arrest of the fresh phone hacking investigation. Like his colleagues, he is currently part way through a 90-day consultation period after the paper was closed on July 10 amid growing political and financial pressure over the hacking scandal.
Responding to reports that the leak had been made to the Guardian, a spokesman for the newspaper said: "We note the arrest of a Scotland Yard detective on suspicion of misconduct in a public office relating to unauthorised disclosure of information. On the broader point raised by the arrest, journalists would no doubt be concerned if conversations between off-the-record sources and reporters came routinely to be regarded as criminal activity. In common with all news organisations we have no comment to make on the sources of our journalism."