He has been declared bankrupt, his political career lies in tatters, and now Rod Culleton is on the hook for hundreds of thousands of dollars to the Federal Government.

A letter from the Finance Department advised him he was legally required to pay back his $200,000-a-year salary he earned as a senator, plus what he paid his staff and other expenses, because the High Court found he was never eligible to run for election.

"It's saying all expenses, I think right down to all the stationery in the office," he told AM.

The letter advised Special Minister of State Scott Ryan can waive the debt.

Senator Ryan told Sky News he did not want to "prejudge" the matter.

But he said the Department of the Senate and the Finance Department had sent letters to both Mr Culleton and former Family First senator Bob Day.

"As I understand it, because those letters have not come from me, the debts have not yet been raised," Senator Ryan said.

"But there's a process to go through that any citizen can apply for about the waiver for a debt to the Commonwealth."

The Finance Department can also decide not to pursue the debt, and the letter suggests Mr Culleton go about "… providing evidence of your financial circumstances for consideration by the departments in determining what actions to take, noting we understand you have recently been declared bankrupt".

Culleton vows to take legal fight to Privy Council

Despite the conciliatory tone and the long-standing legal requirement for the Department to create the debt and write to Mr Culleton, he said he was the victim of a politically motivated attack.

"What it's doing is setting a really bad case precedent that anyone that wants to get out and do the best and have a voice for their country, this is what can happen, it can have a big recoil," he said.

And he has vowed to take the legal fight to clear his name and resume his political career to the highest court in the British legal system.

"There is an avenue that is clear to write to the Privy Council and I will be doing that," Mr Culleton said.

Legislation passed in both Britain and Australia in 1986 made it virtually impossible for Australian citizens to make applications to the Privy Council to overrule the High Court.

Mr Day was also ruled by the High Court to have been ineligible to sit as a senator for part of his term in Canberra.

He offered a "no comment" when AM asked him if he had been issued a debt notice asking him to pay back his salary and expenses.

"I'm a little bit over things at the moment," he said.