The commission is investigating the force’s use of gangland barrister Nicola Gobbo as a registered police informer who gave information about some of the state’s most infamous criminals, some of whom were her own clients.

Mr Dale had a close association with Ms Gobbo, who he claimed had acted as his lawyer when he was under suspicion and once had an sexual liaison with.

Mr Hannebery said the documents may not have been relevant to the original notice to produce, but Commissioner Margaret McMurdo rejected this, saying the inquiry called for all documents relevant to Ms Gobbo’s work as Informer 3838.

"Can I suggest to you and those instructing you, remind your clients [Victoria Police] that this notice to produce, and their obligations under it, which are ongoing, that it is an offence not to comply with it and an agency of the crown, under the inquiries act, can be charged," Ms McMurdo said.

It was the strongest message from the commissioner in an inquiry that has been frustrated by a struggle to obtain secret documents from the force.

Under the state's Inquiries Act, failing to produce documents without a reasonable excuse or refusal to comply can carry a maximum two years in jail.

The royal commission said if a charge was laid, it would go to Victoria Police as the “state agency” and would be served on the Chief Commissioner’s office, but Commissioner Graham Ashton would not be personally charged.

Victoria Police has argued the sheer volume of documents the force had to check in order to protect other informers, police methodology and active investigations has slowed down its ability to produce documentation.

Counsel assisting the commission, Chris Winneke, QC, said it was "most unsatisfactory".