"We've done that and decided to undertake an investigation, but until we've gathered some material we are unable to say what form the investigation will take or how long it will take."
One of those complainants was Wellington-based Roger Brooking, who was told of the IPCA's decision today by email.
Mr McCready has also now filed charging documents against Prime Minister John Key and the police officer who led the investigation into Banks, Detective Inspector Mark Benefield, claiming the Police had conspired to defeat the course of justice by not prosecuting.
In response, Assistant Commissioner Malcolm Burgess said in a statement that all police staff involved in the John Banks investigation acted professionally and impartially in carrying out the inquiry.
"We have the utmost faith in the integrity of the investigation and the staff involved will be fully supported in any proposed court process."
Labour has called for an independent inquiry into police investigations in politically charged cases and whether there was political pressure in cases such as Banks' and the 'teapot tapes' complaint taken by Prime Minister John Key in 2011.