The Ombudsman has ruled that police got it wrong in withholding a witness statement made by ACT MP John Banks.
Police investigated Mr Banks' electoral returns for his failed 2010 Auckland mayoral campaign and donations that had been declared anonymous.
When they released files from the inquiry, they blanked out his statement to them.
In response to a complaint from the Labour Party, Ombudsman Ron Paterson ruled that police had good reason to refuse parts of the statement, but the decision to withhold it in full was not justified.
Professor Paterson said information from the statement will be released after the court proceedings against Mr Banks are finished to protect the MP's right to a fair trial.
Mr Banks is being prosecuted by the Solicitor-General on a charge of making a false electoral return after police decided not to lay charges.
Labour says it was right to pursue the release of Mr Banks' witness statement. Associate security and intelligence spokesperson Grant Robertson says the statement should have been released from the outset.
"John Banks' witness testimony should be treated the same as the other witnesses in this case. The police had released that material and we felt that it was in the public interest for Mr Banks' material to be released and we're certainly pleased the Ombudsman has agreed with that."
Mr Robertson says the statement can't be made public until legal proceedings against Mr Banks have been concluded.