Graham McCready has said pursuing private prosecutions against a senior police officer and the Prime Minister is not a waste of court time.

The retired accountant laid a prosecution against John Banks after police decided not to charge the former Act MP over his 2010 mayoral campaign donation return.

The Crown later took over the case and after a trial in the High Court at Auckland, Banks was found guilty of knowingly filing a false return over donations from Kim Dotcom that were declared anonymous.

Mr McCready told Radio New Zealand this morning that his latest private prosecutions were against Prime Minister John Key and the police officer who led the investigation into Banks and did not lay charges against him.


He rejected claims the law suits were a waste of judicial time.

"That's not my issues, that's what the courts are there for. I'm not a serial litigant, I'm New Zealand's private prosecutor who is representing the public ... In fact the courts have said that these public prosecutions are a powerful check on the abuse of power by the executive branch of government."

Detective Inspector Mark Benefield, who led the police investigation into Banks, is accused of conspiring with the former MP and others, "probably" including Prime Minister John Key, to defeat the course of justice by not prosecuting.

Another charging document alleges Mr Benefield became an accessory to Banks' offending.

Mr McCready has also laid charging documents alleging Mr Key committed the same offences, while a further charging document has been laid against Banks for allegedly conspiring to defeat the course of justice.

Mr McCready said he believed Mr Benefield and Mr Key could both be found guilty.

"Absolutely I do, because of our independent judiciary."

Like any private prosecution, Mr McCready's will now go through an administrative process, and a district court judge will have to decide whether it should continue.

All police staff involved in the John Banks investigation acted professionally and impartially in carrying out this inquiry, Assistant Commissioner Malcolm Burgess said in a statement.

"We have the utmost faith in the integrity of the investigation and the staff involved will be fully supported in any proposed court process."