The government will also have to weigh up whether its actions will anger One Nation whose four Senators have been largely supportive of its legislative agenda.

Senator Roberts' fate hinges on whether he was ever a British citizen, which he is refusing to disclose, and whether he took all reasonable steps to renounce the citizenship before he was elected.

Senator Roberts, born in India in 1955 to a Welsh father and an Australian mother, told Sky News on Thursday night he wrote to the British High Commission on May 1 last year asking if he was a UK citizen.

Five weeks later, he hadn't received a response, so wrote again on June 6 - three days before nominations closed - saying that if he had British citizenship, he fully renounced it.

Threat to call police

"I've taken all steps that I reasonably believe necessary," Senator Roberts said.

After he was elected on July 2, Senator Roberts said he and his wife kept badgering the High Commission and it was not until December 5 he received a formal registration of his renunciation.

He refused to show any of the letters or documents on camera and is refusing to make them public. He has threatened Fairfax Media he will call the police if its journalists keep sending his office questions.


Sky News host Paul Murray, who was shown the documents, said Senator Roberts does not believe he was ever a British citizen and "the document from the UK makes no suggestion he was".

The government source said if it was ascertained Senator Roberts was a UK citizen, he would most likely be referred to the court. He would have to prove his pre-elections emails met the test of taking all reasonable steps to renounce the citizenship.

Senator Roberts said he had received legal advice suggesting he would survive a High Court case.

"Very confident, and I've received advice legally to the same effect, (I am) very pleased with that advice," he said.