Western Australia's corruption watchdog has signalled possible criminal charges may be laid in relation to an investigation of "grave allegations of serious misconduct" against former members of Parliament.

Key points: The CCC says a laptop could be used as evidence in the misconduct investigation

The CCC says a laptop could be used as evidence in the misconduct investigation The probe has involved documents and emails belonging to three ex-Liberal MPs

The probe has involved documents and emails belonging to three ex-Liberal MPs But a turf war between the CCC and Upper House is heading to the Supreme Court

It comes as the WA Legislative Council voted to start Supreme Court proceedings against the Corruption and Crime Commission (CCC), in an ongoing turf war between the two powerful bodies.

The CCC has provided the Legislative Council with a laptop it seized during a raid on former Liberal MP Phil Edman's home on August 14, after a parliamentary committee demanded the device be handed over.

In a letter tabled in Parliament, CCC Commissioner John McKechnie told Legislative Council President Kate Doust the laptop and its contents were "significant to the Commission's investigation and the denial of the data to which the Commission is lawfully entitled will adversely impact the progress of the investigation".

"The laptop may be used as evidence in a possible criminal prosecution in the future," Mr McKechnie wrote in the letter, dated September 4.

Leader of the Upper House Sue Ellery has tabled in Parliament a bundle of letters from Mr McKechnie to Ms Doust.

The letters relate to a row between the CCC and the Legislative Council over emails and documents belonging to three former Liberal MPs, which were handed to the corruption watchdog as part of its investigation into electoral and other allowances.

Letter reveals laptop handed over

In a letter to Ms Doust in July, Mr McKechnie wrote the CCC was "investigating grave allegations of serious misconduct against former members of Parliament".

In a separate letter, he noted the Commission did not know when it executed a search warrant on Mr Edman's home that he had kept the computer — issued to him by the Department of Premier and Cabinet (DPC) as an MP — when his term of office finished.

Former South Metropolitan Region MP Phil Edman says he maintains his innocence. ( ABC News )

The Procedure and Privileges Committee yesterday demanded the corruption watchdog return the laptop and any copies of documents on the device.

Yesterday, Mr McKechnie wrote to Ms Doust to notify her the laptop had been handed to the Legislative Council.

He also enclosed a DPC portable hard drive which was also seized from Mr Edman's home and "which appears to contain the backup of the DPC laptop".

"The laptop contains thousands of documents, some of which have already been identified as relevant to the Commission's investigation and which will not be subject to parliamentary privilege," Mr McKechnie wrote.

Speaking after the letters were tabled in Parliament, Mr Edman said he maintained his innocence.

"I feel there is something else behind all of this, pushing this agenda, and I would like to know what it is," Mr Edman said.

Turf war between CCC and Upper House deepens

The turf war between the committee and the CCC centres on access to emails and documents belonging to former MPs which may be covered by parliamentary privilege.

The stoush has pitted the Premier and his department against an Upper House committee. ( ABC News )

It is also is investigating whether the department's director general Darren Foster and his deputy Emily Roper were in contempt of Parliament or breached parliamentary privilege when they complied with that order from the CCC.

The committee argues that only Parliament, and not the DPC, had the right to determine which documents were covered by parliamentary privilege and could be given to the CCC.

In an action called for by the committee, the state's Legislative Council has now voted to start proceedings against the CCC in the Supreme Court, to challenge the corruption watchdog's right to have ordered the Premier's department to provide the documents in the first place.

Ms Ellery told the Upper House it was an argument between Parliament and the CCC about how the watchdog conducted its investigations.

She said it was not fair to embroil Mr Foster and Ms Roper in that because they were caught between being in contempt of the CCC's orders or in contempt of Parliament.

She also said the investigations against them should be dropped.

Education Minister Sue Ellery wants investigations into two DPC employees dropped. ( ABC News: Marcus Alborn )

Deputy chair of the committee and Upper House Liberal MP Simon O'Brien denied accusations by Premier Mark McGowan that the committee or the house were trying to frustrate a corruption investigation.

"What it is about is an agency of government seeking to change our rules to suit themselves," he said.

"So what this resolution is about is the Parliament seeking to assert its authority."

"This house needs to reassert its view that matter which is covered or subject to parliamentary privilege is not there to be seized or trawled up in those sorts of fishing expeditions, full stop. And that it is unacceptable to do that."