Scotland Yard is investigating claims that its officers took bribes in return for leaking sensitive information from an ongoing criminal investigation.
Anti-corruption detectives have launched a probe into allegations that serving Met officers were paid by private investigators working for an international politician.
Documents sent to the Met and seen by the Evening Standard suggest the high-profile figure hired investigators to obtain information on a police investigation into his business affairs.
The papers allege the London-based private detective agency then paid Met officers £20,000 for inside information that helped his defence lawyers.
A Scotland Yard spokesman said: "We received a complaint alleging that illegal payments had been made to police officers for information (unconnected to phone hacking or the media).
The Directorate of Professional Standards referred the matter to the Independent Police Complaints Commission and they have agreed to supervise a DPS investigation into the allegations."
The Met is already investigating officers for receiving illegal payments from the Murdoch media empire for private information on the royal family.
Scotland Yard has been criticised for its closeness to News International and for failing to properly investigate phone-hacking at the News of the World. The scandal claimed the scalps of two senior Met officers, including Commissioner Sir Paul Stephenson.
Tom Watson, the Labour MP who helped to expose the phone-hacking, said: "This is a very serious development and goes to the heart of the inappropriate relationships between the Met and [private investigators] that have emerged in recent months."
The inquiry was launched after leaked invoices, seen by this newspaper, showed private investigators billed the politician for information from police. One £5,000 payment was allegedly made to a source for information "on forthcoming strategy to be deployed by police".
The Standard understands this was a named Met police detective. Another invoice shows the agency billed the politician £700 for a four-hour meeting about "eliciting feedback... during earlier police interviews".
The politician allegedly hired a well-known City law firm to defend him from the police inquiries. In turn, it hired the private detective agency.
"The Company dealt with telephone/email interception, mobile interception, localised bugging/debugging, any type of record tracing, bank account details, security protection, and more importantly provided intelligence and information on the progress of police...activity," a whistleblower claims.
The Evening Standard has been told the names of the alleged corrupt police officers, the international politician and the private detective agency but cannot name them for legal reasons.
COULD THE INTERNATIONAL POLITICIAN BE : GORDON BROWN ?