The police chief in charge of the phone-hacking investigation spoke of her anger tonight 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 yesterday 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.
A News International spokeswoman said: "We are fully co-operating with the police investigation and we are unable to comment further on matters due to ongoing police investigations."
The arrests came after it emerged Glenn Mulcaire, the private investigator jailed over his work for the paper, was taking legal action against News International.
Mr Mulcaire, who was jailed for six months in 2007 for intercepting messages on royal aides' phones, has lodged papers at the High Court.
A spokeswoman for News International, which owned the now-defunct Sunday tabloid, confirmed the action was being taken, adding that "the claim will be vigorously contested".
James Desborough, the former US editor of the News of the World, was quizzed by police over phone hacking yesterday before being released on bail until October.
Operation Weeting, Scotland Yard's fresh investigation into phone hacking, was launched in January.
A series of high-profile figures have been arrested, including former News International chief executive Rebekah Brooks and ex-Downing Street communications chief Andy Coulson.
The scandal has already caused the closure of the News of the World after 168 years and the resignation of Commissioner Sir Paul Stephenson and Assistant Commissioner John Yates.