Four people, including three serving policemen, have been bailed after they were arrested by detectives investigating alleged fraud involving the organisation that represents rank and file officers.
The probe into an allegation of "potential fraudulent activity" was sparked after the Police Federation of England and Wales (PFEW) raised concerns with police on Tuesday.
A day later a formal allegation was made relating to accounts held by the Federation's Constables' Central Committee.
Surrey Police, which is investigating, said the allegation "relates to concerns about the transfer of around £1 million to a charitable account in August 2015".
The force said two men in their 50s and two men in their 40s were arrested on Friday morning on suspicion of fraud under Section Four of the Fraud Act and conspiracy to defraud.
Three of those arrested are serving police officers.
The force said on Friday night that all four have been released on bail until June while the investigation continues.
Detective Superintendent Karen Mizzi, who is leading the inquiry, said earlier: "We are carrying out a detailed and thorough investigation into allegations of fraudulent activity involving significant amounts of money."
She added: "The Police Federation reported the matter to us as their headquarters in Leatherhead and we are their local force, but to be clear those arrested are not Surrey Police officers."
The Police Federation represents tens of thousands of officers of constable, sergeant and inspector rank.
In a statement on its website, the organisation said it is "co-operating fully" with the inquiry and "gives Surrey Police its utmost support".
It added: "The day-to-day running of the PFEW is not affected and the PFEW remains committed to representing its 122,000 members.
"Until the inquiry is complete, it would be inappropriate to comment further."