A high criminal threshold for corruption is hampering accountability as "grey or soft corruption" and improper conduct by ministerial advisers often goes unpunished, according to a former watchdog.

Former Victorian ombudsman Deborah Glass said ministerial staff remain unaccountable as she pointed to numerous examples of misconduct that failed to reach a high legislative threshold of criminal corruption.

One investigation into the state Labor Party found it misused $400,000 of taxpayer funds to pay for political campaigning at the 2014 election and included the sign off of more than 20 Labor MPs.

"The scheme was an artifice and it was wrong ... but I did not conclude that it was criminal," she told an anti-corruption commission conference in Melbourne on Tuesday.

"In short, nothing happ

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