Suspected dual-national politician Susan Lamb has broken her silence to claim she has been cleared by UK authorities.

The Government is threatening to send the Labor MP and at least one other colleague to the High Court over their citizenship.

The Queenslander's deceased father was born in the United Kingdom.

Ms Lamb said she applied to the Home Office in May 2016, only to receive a letter in August saying it could not process the renunciation.

"We have received your reply to our request [for additional documents] but we cannot be satisfied from the documents available that you hold British citizenship," the letter said, according to Ms Lamb's office.

"The application [to renounce citizenship] has therefore been refused."

Further documents requested 'could not be provided'

A spokesman for Ms Lamb said British authorities requested further documents — such as her parents' marriage certificate — but the certificate could not be provided.

Ms Lamb is estranged from her mother.

The Member for Longman said she had taken "all reasonable steps" to sever any UK ties, fulfilling the High Court's requirements.

"I completed the application to renounce, organised payment of 272 British pounds, [and] sent that by registered post in May to the UK Home Office," Ms Lamb said.

"Records show that payment was processed on the 6th of June.

"I then nominated the day after on the 7th of June.

"What landed back to me in my post box was a letter from the UK [Home Office] saying they are not satisfied I'm a British citizen.

"I can't force the UK [Home Office] to process to renounce something they're not satisfied that I hold."

Ms Lamb's office has refused to provide a copy of the Home Office letter to ABC News.

Before the 2016 election, politicians had to renounce citizenship by June 9 to guarantee their eligibility.

But Lamb's eligibility 'still in doubt'

Constitutional law expert Anne Twomey said Ms Lamb was still in doubt — with two key questions yet unanswered.

"The first is whether or not she actually was a dual citizen at the time of nomination," Professor Twomey said.

"The problem seems to be the British Government didn't have enough information to know.

"The second issue is whether taking all reasonable steps before nomination is enough.

"That's one that's unresolved, that the High Court will need to decide upon."

Susan Lamb (right) said she has been "constantly bullied" by the Government. ( ABC News: Nick Haggarty )

Lamb says she was 'bullied, intimidated' by Turnbull

ABC News repeatedly tried to speak with Ms Lamb after her eligibility came into doubt.

The Sunshine Coast MP said the introduction of a Parliament-wide citizenship register allowed her to speak freely about her situation.

"In a position where I was being constantly bullied by this Government, it was just time to release the documents," she said.

"I'm a little bit over being bullied and intimidated by this Prime Minister around this.

"Let me get on with the job I was elected to do."