A serving Scotland Yard officer was arrested today on suspicion of receiving illegal payments from journalists.
The 52-year-old woman, understood to be a member of the force's specialist operations branch, is being held in Essex after detectives swooped on her home at dawn.
She is the first police officer arrested under Operation Elveden, the inquiry into alleged illegal payments, which runs alongside the Operation Weeting phone-hacking investigation.
The specialist operations division in which she works covers some of the Met's most demanding roles, from counter-terrorism to protecting the Royal Family.
The suspect was arrested at her home less than a week after officers questioned former News of the World crime editor Lucy Panton over alleged payments.
A Scotland Yard spokesman said she was arrested at 6am.
"Officers from Operation Elveden arrested a serving Metropolitan Police Service officer on suspicion of misconduct in a public office and offences contrary to the Prevention of Corruption Act 1906," a force statement said.
"The 52-year-old woman was arrested at a residential address in Essex and is currently in custody at an Essex police station."
Eight suspects have now been arrested as part of Operation Elveden, which was launched after officers were handed documents suggesting News International journalists had made payments to officers.
Ms Panton, 37, who is married to a Scotland Yard detective, was questioned and later bailed after officers swooped on her Surrey home last Thursday.
Others questioned as part of the inquiry include former News International chief executive Rebekah Brooks, ex-Downing Street communications chief Andy Coulson, former News of the World managing editor Stuart Kuttner, the paper's former royal editor Clive Goodman, and a 63-year-old man whose identity has not been disclosed.
Mrs Brooks and Mr Coulson are both former editors of the News of the World, which was closed in July at the height of the hacking scandal following revelations that murdered teenager Milly Dowler's phone was involved.
Elveden was launched in the summer after News International handed documents to Metropolitan Police officers.
Sir Paul Stephenson, the then Met commissioner, said in July that evidence from the publisher suggested a small number of officers were involved.
The final total of people whose phones were hacked by the News of the World will be about 800, the force believes.
The scandal has led to the closure of the News of the World after 168 years, prompted a major public inquiry, and forced the resignation of Metropolitan Police commissioner Sir Paul and assistant commissioner John Yates.