Police are planning to deploy 80 detectives for their criminal inquiry into the Post Office scandal, the Guardian has learned, but victims will face a long wait to discover if charges will follow.

The investigation will examine potential offences of perjury, and perverting the course of justice by Post Office senior leaders as well as the tech company Fujitsu.

Police have already started discussions with prosecutors about the investigation and potential criminal charges, which stem from the possibility that post office operators were wrongly prosecuted for stealing when bosses allegedly knew their computer accounting system could be flawed.

The police operation will be national and split into four regional hubs. The staffing and resources will be similar to a major murder or terrorism investigation. Police have asked government for a special grant of at least £6.75m to fund the operation.

But the victims face a big delay before finding out if those who pursued them – they say wrongly – will themselves face criminal trials.

Police will not seek charging decisions, that is send files of evidence to the Crown Prosecution Service, until after the public inquiry into the Post Office scandal concludes, which is expected in autumn 2025.

It is expected the CPS will not reach charging decisions until 2026, and the wait for any criminal trials could be even longer. Detectives and civilian analysts are yet to be recruited, with the start of the full national police investigation months away.

Early work has identified at least 20 potential suspects, but more could follow as the criminal inquiries get fully under way. One source said there could be dozens of potential suspects.

The team, once up and running, will consider whether the offence of fraud should also be added to the list of offences that should be examined. The special case work division of the CPS is advising police on the Post Office investigation and deals with complex cases.

Since 2020, the Metropolitan police has been leading the investigation but the scale of the potential crimes and the fact so many cases are outside the London area has led to the plan to establish a national operation.

Stephen Clayman, the Met commander, said: “A team of detectives has been painstakingly working through millions of documents manually and with the help of specialist software, in parallel with the public inquiry.

“This is very time-consuming and we cannot cut corners and risk missing evidence.

“Given the significant scale of the investigation, it has been agreed by the National Police Chiefs’ Council (NPCC) that the next phase of the investigation will be a national policing effort, coordinated by the Met, with the pursuit of justice at its heart.”

It is expected the plans for the national investigation will go to the police chief’s decision making body, called the National Police Chiefs’ Council, to be approved.

The new national phase of the police investigation will be overseen by a senior officer, most likely the Met assistant commissioner, Louisa Rolfe.

More than 900 sub-post office operators were prosecuted between 1999 and 2015 after errors in the Horizon software system wrongly showed money missing from their branches.

Some were jailed, pursued for money, financially ruined and in some cases so broken by the pressures and injustice they took their own lives. The Post Office continued to fight those who were wronged until 2019.

A new law has exonerated some of those convicted and they will be entitled to final compensation of £600,000, or can accept an interim payment and keep their legal options open.

The public inquiry is examining: “The non-disclosure by Royal Mail Group Limited / Post Office Limited of the existence of problems with and / or concerns about the reliability of Horizon when bringing criminal proceedings against persons alleged to be responsible for those shortfalls.”

It is also examining: “At what level within the organisations named and the government were these known?”

Police have been closely monitoring the evidence, verbal and in writing, at the public inquiry.