The real identities of Nicola Gobbo's handlers have been accidentally sent to the lawyers of her former underworld clients by the royal commission that is investigating her role as a police informer.

Protecting the names of the covert operatives from Victoria Police's Source Development Unit is one of the most sensitive issues at the Gobbo inquiry amid concerns about potential retribution against those who recruited and ran the supergrass.

Lawyer-turned-police informer Nicola Gobbo.

Commissioner Margaret McMurdo has authorised a series of suppression orders and extensive document redactions to prevent the release of any information that might identify former SDU members, assigning each a pseudonym.

But in what some police regard as a serious security breach, a list linking the officers' real identities to their pseudonyms was accidentally emailed to the legal teams for up to 20 of Gobbo's former clients whose convictions have been called into question by her dual roles as a barrister and police informer.