A review of News Ltd’s major newspapers has found no evidence of illegitimate phone surveillance or payments to public officials, the media company says.

The three-month review was commissioned by News Ltd chief executive John Hartigan, and carried out by a team of 26 auditors.

The auditors scrutinised almost 700,000 transactions carried out over a five-year period.

Retired Victorian Supreme Court judges Frank Vincent and Bernard Teague, appointed as independent assessors of the review by the Australian Press Council, said on Monday they had no reason to suspect the review was not conducted “as assiduously as indicated to us”.

“The review’s findings provide the strongest possible support for News Limited’s assertion that its editorial staff have not commissioned the kind of illegitimate surveillance or payments that have come to light in the UK,” News Ltd said in a statement.

News Ltd papers include The Australian, the Courier-Mail, The Daily Telegraph, The Sunday Telegraph and the Herald Sun.

“I said at the start of this process I had no reason to suspect any wrongdoing,” the soon to retire News Ltd chairman and chief executive John Hartigan said in a statement on Monday.

“An incredibly diligent piece of work has confirmed that.

“Nevertheless, we will use this opportunity to put in place measures to further reinforce our standards.”

News Ltd would adopt a single code of conduct across all its editorial operations and further strengthen the approval process for any use of private investigators, the company said.

A procedure would be put in place to ensure all editorial staff renewed their knowledge of the code of conduct each year.