The High Court has heard Labor Senator Katy Gallagher's submission in defence of her eligibility for parliament "ignores almost entirely" the wording of section 44 of the constitution.
Solicitor-General Stephen Donaghue's submission in the Gallagher case was published on Friday ahead of the full court hearing the matter in Canberra on Wednesday.
The ACT Labor senator could be disqualified from parliament if the court finds her ineligible due to her holding British citizenship in 2016.
She completed a declaration of renunciation of her British citizenship on April 20, 2016, and the UK Home Office deducted a fee for the registration on May 6 - 10 days before the issuing of writs for the federal election.
Her lawyers cite experts saying the material provided on April 20 was "sufficient there and then" to satisfy the requirements imposed by the law of Britain for cessation of her citizenship.
However, the UK Home Office asked Senator Gallagher on July 20, weeks after election day, to provide originals of her father's birth certificate, her parents' marriage certificate and her own birth certificate.
The lawyers said providing these extra documents was "an additional layer of proof" of the information already provided, and something not reasonably required under British law.
However, Mr Donaghue said Senator Gallagher's submissions were "striking for ignoring, almost entirely, the words of section 44 (i)" of the constitution, which deals with citizenship issues.
He said on Senator Gallagher' argument it would be open to a candidate for election to refuse to provide further information to a foreign office if requested, remain a foreign citizen and yet not be disqualified from parliament.
"If the steps taken by Senator Gallagher are relevant, they were inadequate because it was lawful and reasonable for British officials to take the course they did and to require more information to be provided before registering her declaration," the submission said.
Guidance material provided by British authorities should have alerted her to the need for more evidence in her application.
Rather than "oppressive delay" or "arbitrary exercises of power", the court had heard in a number of MP citizenship cases that renunciations could be completed within periods of days or a few months, Mr Donaghue said.
"It is a plea to the court to 'shut [its] eyes and grope in the dark', which should not be entertained," he said of the senator's case.