The citizenship register for senators shows ACT Labor senator Katy Gallagher was still a dual citizen of the United Kingdom when she nominated for the last federal election.

Key points: Labor senator Katy Gallagher took the steps required to give up her UK citizenship before nominations closed

Labor senator Katy Gallagher took the steps required to give up her UK citizenship before nominations closed Senator Gallagher says she does not believe she needs to be referred to the High Court but will leave the decision to the Senate

Senator Gallagher says she does not believe she needs to be referred to the High Court but will leave the decision to the Senate Labor's Doug Cameron was potentially eligible for Lithuanian citizenship but chose not to apply for it

Despite her dual citizenship, Senator Gallagher is refusing to refer herself to the High Court to decide if she was ineligible.

She said had taken the steps required to give up the UK citizenship she acquired through her father before nominations closed.

But she did not receive the letter from the UK Home Office confirming her renunciation until August 16 last year, which was two months after nominations closed.

The Prime Minister has said that Labor figures like Senator Gallagher who did not renounce other citizenships before the election should be referred to the High Court to decide their eligibility.

Senator Gallagher said she took all necessary steps to renounce British citizenship, including paying the processing fee.

She said she had received legal advice, including from an expert on British nationality law, which said she had taken all necessary steps.

Senator Gallagher said on Facebook she did not believe she should refer herself to the High Court, but conceded it would ultimately be a matter for the Senate to determine.

Her mother was born in Ecuador in 1943 to British parents, but Senator Gallagher said she was not and had never been an Ecuadorian citizen.

Cameron could be eligible to become Lithuanian

Doug Cameron's documents show he may also be eligible for Lithuanian citizenship. (AAP: Mick Tsikas)

The citizenship released today reveals that Labor senator Doug Cameron is potentially eligible for Lithuanian citizenship.

Senator Cameron was born in Scotland and renounced his British citizenship before nominating for Parliament.

His form shows his maternal grandparents left Lithuania for Scotland before his mother was born in 1915.

Last year, Lithuania changed its laws to allow for dual citizenship for descendants of Lithuanian citizens who left the nation before 1940.

But Senator Cameron said to acquire Lithuanian citizenship he would have to apply and he confirmed he had not done so.

Greek parents and an 'immaculate conception'

Liberal senator Arthur Sinodinos and One Nation's Peter Georgiou both had parents born in Greece, which might give them Greek citizenship by descent.

Senator Sinodinos said he had legal advice confirming he was not a Greek citizen and was not entitled to it.

He tweeted a letter from the Greek Government supporting that stance.

Senator Georgiou provided a document from the Greek Embassy showing he could not be considered a Greek citizen.

Liberal Democrat senator David Leyonhjelm's form shows all his parents and grandparents were born in Australia.

But in the section that asks for other relevant information, he wrote "I once asked my mother if my father was truly my father, but she was offended so I didn't ask again".

"I suspect immaculate conception."

Members of the House of Representatives have until tomorrow to present their citizenship documents.

Every citizenship declared

These are the citizenships Senators have claimed to renounce.

This article contains content that is only available in the web version. Open the web version