Tasmanian Greens senator Nick McKim is seeking proof from the British Government that he is no longer a UK citizen, but remains confident he has met senate requirements.

In the wake of Greens senators Scott Ludlam and Larissa Waters resigning after discovering they were dual citizens, other members of Federal Parliament born overseas are scrambling to prove they are 100 per cent Australian.

Senator McKim was born in the United Kingdom and came to Australia as a child.

He said he wrote to Britain's Home Office in 2015 to renounce his citizenship before entering the Senate on a casual vacancy left by Christine Milne.

"I'm an Aussie and an Aussie alone," he told ABC Radio Hobart.

"What I've got is the letter I sent to the United Kingdom Home Office which renounced my citizenship."

According to British rules, if an application to renounce citizenship is accepted, a declaration of renunciation is provided.

But Senator McKim conceded he did not receive one.

"I did not receive anything back from the UK Government and we're asking for that because I think that's what people want to see," he said.

"The test the High Court has applied in cases where people's right to sit in the Commonwealth Parliament has been challenged is that a person simply needs to do everything possible to renounce.

"I got legal advice at the time. I'm very confident I've met that test."

Senator McKim committed to releasing the correspondence from the United Kingdom Government publicly when he received it.

Tasmanian Labor Senator Lisa Singh has revealed she had a citizenship "near miss" just days before entering Parliament.

Senator Singh's father came to Australia from Fiji as a British subject.

"I was lucky the Labor Party did the work because, despite being born in Australia, I was shocked to find out that I was also a British citizen, through my father," she said.

"His British citizenship that he still held when I was born was conferred on me through birthright — so I had dual citizenship that I never knew about.

"I had to pay 300 pounds to the British High Commission to urgently rescind my British citizenship — which was confirmed just three days before I was elected."