The former head of the Australian Border Force has come forward with explosive new evidence in the inquiry into Home Affairs Minister Peter Dutton, telling the Senate of a phone call from the minister’s office to seek the release of an Italian au pair from detention.

Former Border Force commissioner Roman Quaedvlieg wrote to the Senate inquiry to reveal the phone call he received from Mr Dutton’s chief of staff in June 2015, seeking help for a "mate" of the minister who had an au pair in detention at Brisbane Airport.

While Mr Dutton told Parliament in March that he could rule out any personal connection to the family who hired the au pair, the new evidence draws attention to the friendship as a reason for the minister’s intervention.

Former Australian Border Force Commissioner Roman Quaedvlieg has intervened in the Senate inquiry into Home Affairs Minister Peter Dutton. Credit:Alex Ellinghausen

Fairfax Media revealed last week that Mr Dutton made the intervention after a request from one of his former colleagues in the Queensland Police, Russell Keag, but that the two men had not spoken for about 20 years.