One Nation senator Malcolm Roberts insists he is eligible to sit in Parliament, but is still refusing to release documents proving he has renounced his British citizenship.

Key points: Malcolm Roberts was recorded as a British national in the past

Malcolm Roberts was recorded as a British national in the past Senator releases statutory declaration denying he's a dual citizen

Senator releases statutory declaration denying he's a dual citizen Roberts has been pushing for a review of the eligibility of all parliamentarians

Senator Roberts was born in India and his father was Welsh, but he denies he is a dual citizen.

He has released a statutory declaration after coming under pressure to clarify his status, due to the resignation of two Greens senators with dual citizenship and Matt Canavan quitting the Cabinet for the same reason.

In the declaration, Senator Roberts said he had, "analysed if he was a British [United Kingdom] citizen by decent [sic] from my father, who was born in Wales, the United Kingdom, or if I was an Indian citizen".

"I can confirm I am not a citizen of the United Kingdom, nor am I a citizen of India," he wrote.

But he has not backed that up with any other documents, although he said on Twitter he has them.

Birth records available online show Senator Roberts was recorded as a British national in the past, but that would not affect his eligibility if he had subsequently renounced it.

Senator Roberts has not explained why he has not released any paperwork to prove he does not hold another citizenship.

The British High Commission told the ABC: "British nationality law is complex, with a number of factors influencing eligibility, including date and place of birth and citizenship of parents.

"It's not possible for us to comment on specific cases or to speculate more generally on whether or not people might hold British citizenship but if people are unsure they should review the citizenship section on our gov.uk website."

Despite the lack of clarity about his own citizenship, Senator Roberts has been leading the push for a review of the eligibility of all parliamentarians.

"Until the inquiry, my stat dec stands. My renunciation documentation will be provided to this inquiry," he wrote on Facebook yesterday.

This morning, he said he would soon release details of the review, and said he met with the Clerk of the Senate today for advice on the draft text.

One Nation leader Pauline Hanson said the review should be extended to include former senators.

While Senator Roberts is refusing to hand over documents, his One Nation colleague Brian Burston is demanding parliamentarians "who were not born in this country to provide evidence of the renunciation of their former citizenship".

"It shouldn't be too difficult. After all, they would have had to have it when they nominated for candidacy of their respective parties, or for the AEC if they were independents," Senator Burston said.

"Perhaps when we've cleaned out those whose loyalty is not entirely to this country we can start getting things fixed."

Defence Minister Marise Payne also said any parliamentarians facing eligibility questions, including Senator Roberts, should provide evidence they are not dual citizens.

"I would have thought that making the position as clear as possible is the best way to go, I think that's exactly what Minister Canavan did yesterday, and I'd encourage anyone involved in this process to do that," she said.

Senator Payne said while she was not telling any senators what to do, she "would have thought the greater light that is shone, the greater clarity available, the better".