Embattled Labor MP Susan Lamb has hit back at government pressure for her to quit parliament over her dual citizenship, in an emotional speech laying the blame for her failure to produce a vital document on an estrangement from her mother.

But the government was unmoved by Lamb’s tearful explanation, saying it changed nothing – although there was no sign of imminent action to refer her to the High Court.

Lamb, who holds the marginal Queensland seat of Longman, took steps to renounce her British citizenship but the UK authorities required her parents’ marriage certificate, which she did not produce.

The government has threatened to refer her to the court, despite Labor’s opposition.

Some in the government had hoped that if Lamb could be forced to quit quickly without a court case, a byelection could be held in Longman on the same day as the Batman byelection, thus putting maximum heat on Bill Shorten.

But with Wednesday’s announcement of March 17 as the date for the Batman contest and Lamb refusing to resign, that is not going to happen.

Lamb told parliament she had been advised she did not have a legal right to access the marriage document.

Recounting how her mother had abandoned her as a young child, she said: “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.

"I don’t remember every detail of what happened afterwards. I remember lots of tears. I remember lots of confusion. I remember my dad trying to explain. I remember sometime later, dad taking me to the train station, late one evening, to collect my mother.

"I thought she was going to come home. The train came, the train went, no sign of her, so we went home. Then one day, I remember going outside the front of the mill gates. We lived on the mill grounds in Mackay in north Queensland …

"A car turned up … my mother got out, words were exchanged and then my mother drove away. My dad was now a single parent – an amazing man whose example I try to live up to every day of my life.”

Her father died nearly 20 years ago.

Lamb said many years ago she and her mother attempted to build a relationship, but that failed.

“The fact is, my mum is not around to grant me access to her marriage certificate.”

Lamb said she was not telling the story to gain sympathy, but to explain that she did not have the legal entitlement to obtain the document. “So I would simply ask those opposite, take a moment and think about the circumstances.”

But government sources said that in her situation she could have applied to the registrar of births, deaths and marriages, or have got a lawyer to be an intermediary.

The sources said Lamb’s circumstances were similar to those of former senator Fiona Nash, also British through her father, who sought referral to the High Court and was declared ineligible to sit. Nash’s parents, now both dead, had divorced, and she had had little contact with her father.

Previously The Australian quoted Lamb’s mother saying she would have “definitely helped her if she had been contacted”.

The ABC’s Jane Norman tweeted “Re. Susan Lamb: QLD’s Registry of Births, Deaths and Marriages says requests are considered on a case-by-case basis where parental consent isn’t obtainable”.

Michelle Grattan does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.