In a tearful statement to Parliament, Labor backbencher Susan Lamb has explained she is not legally allowed to have access to her parents' marriage certificate that could clarify her citizenship status.

Key points: Susan Lamb's father died 20 years ago and she is estranged from her mother

Susan Lamb's father died 20 years ago and she is estranged from her mother She says she can't get access to her parents' marriage certificate

She says she can't get access to her parents' marriage certificate The Government says it won't stop chasing her over her citizenship status

In a bid to fend off Government attacks that she is a British citizen and ineligible to be in Parliament, Ms Lamb spelled out that she has been estranged from her mother since she was a six-year-old girl.

"It is a complex and a traumatic story — a story that I don't usually share," she told the House of Representatives.

"One day when I was around six years old my mum dropped me off at school and she never came back to pick me up."

She said her father brought her up as a single parent from that time on, but that he died 20 years ago so she no longer had contact with anyone who was allowed to access the marriage certificate.

The backbencher said she imagined her mother carried her own share of pain and trauma.

"If it is anything like mine, I would not wish that on anybody," Ms Lamb said.

"I don't speak about this trauma. So when people ask me why I couldn't just call my mother, well, this is why.

"I hope this story gives you the answer."

Susan Lamb's colleagues stood in solidarity with her after the statement was finished. ( ABC News: Nick Haggarty )

Ms Lamb has been facing questions about her eligibility because the British Government asked her for more information before it would approve her move to renounce her UK citizenship.

The lack of documentation means questions remain about Ms Lamb's eligibility.

A spokesperson for the Queensland registry of Births, Deaths and Marriages said that where an application falls outside its policy, "for example where parental consent may not be obtainable, the Registrar-General considers such requests on a case-by-case basis".

Ms Lamb's spokesperson did not clarify what specific steps she had taken to obtain the document.

Ms Lamb became emotional while talking about her family history. ( ABC News: Nick Haggarty )

It is understood the Government will continue to insist that Ms Lamb's difficult personal circumstances do not excuse her from having the case heard by the High Court.

"I am very sorry to hear of her personal circumstances and clearly it is very painful for her," Human Services Minister Michael Keenan said.

"But it doesn't actually change the fundamentals of the case at all.

"It really remains up to the Labor Party about what they are going to do about that. We have had members in very similar positions and ultimately they referred themselves to the High Court."