Prosecutors are providing "early investigative advice" to police forces as they inquire into Andrew Mountbatten-Windsor and Lord Peter Mandelson's links to sex offender Jeffrey Epstein.
The Crown Prosecution Service (CPS) said it was providing early investigative advice to the Metropolitan Police regarding its investigation into a 72-year-old man, and to Thames Valley Police in relation to a 66-year-old man.
Mountbatten-Windsor and Lord Mandelson have separately been arrested on suspicion of misconduct in public office over their connections to the paedophile and have both since been released under investigation.
Mountbatten-Windsor has repeatedly denied any wrongdoing in relation to Epstein.
The BBC understands Lord Mandelson's position is that he has not acted in any way criminally and that he was not motivated by financial gain.
A CPS spokesperson said: "We can confirm that we are now providing early investigative advice to the Metropolitan Police Service regarding the force's investigation into a 72-year-old man and will continue to liaise as requested.
"We can now also confirm that we are providing early investigative advice to Thames Valley Police in relation to a 66-year-old man."
Early investigative advice is a routine part of many police investigations - particularly in serious, complex and high profile cases.
It allows CPS lawyers to give views and advice to officers about the evidence they have gathered and that advice typically helps to form an action plan to progress enquiries.
Early investigative advice does not, in itself, indicate that sufficient evidence exists to put someone before the court.
It is not the same as referring a case to the CPS for a charging decision, which typically comes when the police feel they have gathered sufficient evidence to formally ask prosecutors for authorisation to charge.
Mountbatten-Windsor, 66, was released under investigation by Thames Valley Police in February following his arrest at Sandringham.
Prior to his arrest, police had said they were considering investigating him over allegations relating to his association with Epstein and were reviewing allegations he shared confidential material.
Communications between Mountbatten-Windsor and Epstein featured among a tranche of files released by the US Department of Justice.
The former Duke of York served as the UK's trade envoy between 2001 and 2011, enjoying privileged access to senior government and business contacts around the world.
