An anti-corruption investigation has found staff in the Daniel Andrews’ government exerted pressure on health department officials to award a contract to a health union.

The Independent Broad-based Anti-corruption Commission released its Operation Daintree report on Wednesday, after investigating the awarding of the contract worth more than $1 million in the lead-up to the 2018 election.

The investigation substantiated that a ministerial advisor working in the health minister’s office exerted pressure on Department of Health and Human Services staff to award the contract to a Health Workers Union entity.

It also found that an advisor in the office of a subsequent health minister and an advisor in the office of Premier Daniel Andrews intruded into the department’s management of the contract against the public interest.

While there was no corrupt conduct detected, the investigation did reveal “concerning conduct and omissions in breach of the public duties and ethical obligations of ministers and ministerial advisors”.

Conduct by senior public servants also fell short of that required by Victorian standards, the inquiry found.