Police have raided three football clubs as part of an investigation into alleged corruption.
Newcastle United, Portsmouth and Rangers are the three clubs involved in Monday's raids.
Police insisted the operation was "not informed or influenced" by Lord Stevens's ongoing Quest inquiry into the Premiership.
But sources close to the Quest team told the BBC they had passed on information about 17 player transfers.
It is believed that information related to three clubs - Newcastle, Portsmouth and Middlesbrough.
Police revealed search warrants were executed on premises at Newcastle, Portsmouth and Rangers, and two homes, between 0730 and 0900 BST on Monday.
A City of London Police spokesman said: "We can confirm that search warrants were served at three football clubs and the homes of two individuals in connection with corruption in football and its impact on owners and shareholders."
Newcastle United issued a statement confirming the club was visited by police.
"The club itself is not the subject of the investigation," it said.
"If the investigation by the City of London Police, or the ongoing internal review of operations by the club's new owners, show that the club has been the victim of any criminal activity, the club will take appropriate action."
A Northumbria Police spokesman said they were aware that "an operation" had been carried out by their London colleagues at St James' Park, the home of Newcastle United.
A spokesman for Rangers said: "Rangers football club was asked to co-operate with a police investigation and have done so, extending every co-operation to police.
"We have been requested by police not to comment further while the investigation is on-going."
Strathclyde Police confirmed that its officers had executed a search warrant on behalf of City of London Police.
Gary Double, director of communications at Portsmouth, said on Monday: "We can confirm police arrived around 10am today.
"We have co-operated fully with their search and will not be commenting further."
Detectives from the economic crime unit at City of London Police are investigating allegations of corruption within football and its impact on owners and shareholders.
Last month, they arrested a 61-year-old man in Manchester on suspicion of money laundering.
BBC sports editor Mihir Bose added: "The police have had a lot of information on the 17 transfers the Lord Stevens inquiry looked into - all that evidence was given to the City of London police.
"We have also learned the 17th transfer, because there were 17 in total, is being looked at by another government authority."
He added: "Newcastle United is keen to distance itself from any suggestion the club is subject to investigation. Portsmouth and Rangers have acknowledged the raids have taken place."
In June this year, Lord Stevens presented his final report following the the Quest inquiry and highlighted 17 transfers, including four Newcastle deals.
Two of the four transfers named by Lord Stevens took place in January 2005 and involved the other two clubs raided - Jean Alain Boumsong's move from Rangers to Newcastle for £8m and Amady Faye's transfer from Portsmouth to Newcastle for £2m.