Twenty-two men have appeared in court charged with a long list of offences, including illegally accessing the police national computer.
They face claims of conspiring to tap phones and modify computer material.
The accused include former police officers and are on bail ahead of their trials early next year.
A US businessman Matthew Mellon, 42, from London, faces a single charge of conspiring to cause unauthorised modification of computer material.
Prosecutors say most of the men in the dock at Southwark Crown Court either worked for an investigative agency, or were their clients.
'Number of trials'
Miranda Moore, QC, prosecuting, told the case management hearing at Southwark that a number of defendants would apply for charges against them to be dismissed in September.
She also explained that the size of the case would mean a number of trials, with the first scheduled to take place on January 15 next year.
"However, I'm not in a position at this stage to say who that will feature," she added.
Staffordshire-based Detective Sergeant John Matthews, 58, who is currently suspended from duty, joined him in the dock.
He is accused of conspiring to commit misconduct in public office by carrying out an unauthorised check on the police national computer.
Also accused of the same offence were former colleagues turned private investigators Anthony Wood, 63, from Stafford, and Gary Flanagan, 41, from Newcastle-under-Lyme, Staffordshire.