It follows an investigation into the conduct of officers from MI5 and MI6.
Although it is expected that no charges will be brought in some cases it is understood the statement will contain other significant information.
The BBC’s home affairs correspondent, Danny Shaw says the fact that the statement has been prepared by the DPP, together with Scotland Yard, is highly significant.
He says it raises the prospect that police investigations are not yet over.
The DPP, Kier Starmer, eventually concluded there was insufficient evidence to charge Witness B.
But he decided that a “wider” investigation would continue into “other potential criminal conduct”.
An inquiry has also examined allegations against an officer from MI6.