The validity of more than 50 past prosecutions by Western Australia's corruption watchdog are in question after a Court of Appeal decision which put in doubt cases it conducted in the Magistrates Court.

Key points: About 51 CCC prosecutions in the Magistrates Court are in doubt

About 51 CCC prosecutions in the Magistrates Court are in doubt CCC chief John McKechnie says those convictions will not necessarily be overturned

CCC chief John McKechnie says those convictions will not necessarily be overturned But he says the CCC will now be able to provide prosecutors with evidence including transcripts

Attorney-General Michael Mischin said he had received preliminary advice on the legal consequences of last week's Court of Appeal decision which ruled the Corruption and Crime Commission had no powers to prosecute a police officer in the Magistrates Court.

Of 121 past prosecutions, he said about 70 had been dealt with by higher courts and were therefore not in doubt, but the remainder had been dealt with by the Magistrates Court and may be open to challenge.

"It is a matter of concern if the commission has not had the power to initiate prosecutions," Mr Mischin said.

"It is the ones in the Magistrate's Court that are surrounded by some doubt and those will have to be dealt with on an individual basis."

In the case considered last week by the Court of Appeal, the police officer was charged with assaulting two men in the Broome lock-up in March 2013.

Charges were laid by the CCC in the Magistrates Court, but the officer appealed, claiming it was an abuse of process.

In his appeal, the officer claimed the Magistrates Court had no jurisdiction in the matter, making the proceedings unlawful.

In its judgement, the Court of Appeal ruled the CCC lacked the authority to commence the prosecution and ordered the prosecution notices be quashed.

Cases should be considered on merit: Attorney-General

Mr Mischin said he was considering both the implications of the decision and the Government's response.

Michael Mischin says it is up to convicted individuals to lodge appeals. ( ABC News: Emily Piesse )

"As to the effect of the decision on historical cases, each one needs to be considered on its merits," he said.

"A defect in the laying of a charge doesn't necessarily mean that a conviction on that charge may be overturned."

Mr Mischin said it would be up to the convicted person to pursue a challenge to their conviction.

But CCC head John McKechnie said he did not believe the ruling would necessarily result in dozens of convictions being overturned.

"Technically, we haven't had the power to prosecute. That does not affect the validity of the evidence that's been put before courts," he said.

Mr McKechnie said Parliament, if it chose to, could legislate to retrospectively grant the required authority to the CCC.

Mr McKechnie says convictions will not necessarily be overturned. ( ABC News: Andrew O'Connor )

He said in 1998, hundreds of Worksafe prosecutions were thrown into doubt when it was found the organisation's commissioner lacked the required powers.

There had been a delay in appointing the commissioner, during which time the authority to initiate prosecutions was delegated to another Worksafe officer.

Subsequently concerns were raised about whether those actions were legal, forcing the then Liberal government to legislate to retrospectively validate the prosecutions.

"Parliament amended the act, and retrospectively fixed it," he said.

Acting Premier Liza Harvey said the implications of the decision would be fully assessed by the joint parliamentary committee which oversees the CCC.

But she said the watchdog had the Government's full support.

"I don't believe we need a massive overhaul of the CCC. This is a technicality around one particular section of the CCC act, and that is why I think that bipartisan committee is the appropriate vehicle to interrogate that legislation," she said.

Ruling has ramifications for evidence: CCC chief

Meanwhile, Mr McKechnie said the most significant part of the Court of Appeal judgement was that it would pave the way for the CCC to significantly widen the evidence it can use to prosecute people suspected of corrupt conduct.

In his judgement, Chief Justice Wayne Martin ruled the CCC could provide prosecutors with evidence gathered during examinations of suspects and witnesses during corruption investigations.

"There was a big attack mounted on the CCC as an abuse of process," Mr McKechnie said.

"The court unanimously dismissed that and in doing so, has greatly enlarged the ability of the CCC to supply the prosecutor with all sorts of material which, until then, had been thought we couldn't supply.

"It is a really important judgement which will have wide ramifications and enable more successful prosecutions, I believe."

The Court of Appeal concluded the CCC "may furnish the DPP or another prosecuting authority with evidence that has been assembled, including the transcript and any other record of the examination evidence given by a suspected witness", and such evidence would be admissible in a prosecution of the witness.

It said the CCC "must provide the DPP or another prosecuting authority with all materials that are required to be disclosed under the CPA [Criminal Procedure Act] where it recommends that consideration be given to prosecuting a suspected witness."

Mr McKechnie said that aspect of the judgement would mean information the CCC had previously considered must be kept from prosecutors, could now be made available.

"That includes the private examinations of suspected persons. This is a big change of the law," he said.

"I am sure lawyers are reading this judgement very carefully and avidly."