Senator Roberts has told Sky News he wrote to the British Consulate before signing his nomination form to stand as a One Nation candidate at last year's election.
The Senator says it wasn't until December last year he received a response confirming he is not a British citizen....but he won't publicly release the documents.
While Malcolm Roberts is confident of his eligibility, former Liberal minister Gary Hardgrave warns his explanation may not stand up to High Court scrutiny.
It follows the citizenship ineligibility of Greens senators Larissa Waters and Scott Ludlam which forced them to quit parliament.
The Greens are calling for an investigation into the eligibility of all members of parliament, following revelations several politicians violated the constitution's clause on citizenship.
Greens leader Richard Di Natale has criticised former Resources Minister Matt Canavan for not resigning from politics altogether after revelations he held dual Italian citizenship.
Senator Di Natale says Senator Canavan's refusal to step down, is damaging the public's trust in the government.
