The result of an investigation into how police dealt with John Banks' campaign donations can't be released.

Police received complaints about Mr Banks failing to properly declare donations following the 2010 Mayoral election, but eventually decided not to prosecute.

A private prosecution was then launched, resulting in a guilty verdict that has since been quashed.

The Independent Police Conduct Authority has finished its investigation into how police handled the case, but says it can't make the findings public, because of the possible retrial of Mr Banks.