An independent workplace investigation into allegations involving broadcaster Martin Devlin found two complaints against him were not substantiated.

The Newstalk ZB host was off-air in May after he "took a swing" at a colleague, before returning to the airwaves for a weekend.

He has since been off-air while an independent investigation into other matters allegedly involving him was carried out. The Herald reported on June 25 that the investigation was complete and being reviewed by NZME.

The investigation, conducted by senior employment lawyer Bridget Smith of SBM Legal, assessed two complaints and found neither was substantiated, NZME staff were told today.

The two allegations related to conduct in the newsroom, staff were told.

NZME, the parent company of Newstalk ZB and the Herald, did not wish to comment.

Devlin has been approached for comment.