Ginni Thomas, the hard-right conservative whose activities have raised conflict of interest concerns involving her husband, the US supreme court Justice Clarence Thomas, has told the committee investigating the January 6 insurrection that she still believes the 2020 presidential election was stolen from Donald Trump.

Bennie Thompson, the Democratic chair of the committee, told reporters following the almost five-hour private interview with Thomas that she held fast to her claim that massive fraud in the 2020 election had put Joe Biden in the White House. When asked by reporters if Thomas still believed that to be true, Thompson replied: “Yes.”

The stolen election conspiracy theory – widely propagated by Trump – has never been substantiated with evidence and has been thoroughly debunked over the past two years.

In an opening statement to the committee, obtained by the New York Times, Thomas also insisted that she and her husband, the longest-serving member of America’s highest court, abided by an “ironclad rule” never to discuss cases coming before him.

“It is laughable for anyone who knows my husband to think I could influence his jurisprudence – the man is independent and stubborn, with strong character traits of independence and integrity,” she said.

But her dogged attachment to Trump’s lie that he was the true winner in 2020, repeated in front of the January 6 committee on Thursday, is certain to further heighten alarm about the impact of Thomas’s unrestrained hard-right activism on the credibility of the supreme court. Clarence Thomas has consistently refused to recuse himself from cases arising from the insurrection at the US Capitol despite his wife’s avid support for attempts to subvert the election result.

Clarence Thomas was the sole justice among the nine members of the panel to oppose an order in January forcing hundreds of White House documents to be disclosed to the January 6 committee. Among those documents were texts sent by Ginni Thomas to Mark Meadows, then White House chief of staff, in the immediate aftermath of the 2020 election urging him to do all he could to overturn Biden’s victory.

Ginni Thomas has also been exposed as having pressurized lawmakers in Arizona and Wisconsin, demanding that they block certification of Biden’s win in those states in an effort to swing the outcome to Trump.

After the encounter with the committee, her lawyer said she had happily communicated with them “to clear up the misconceptions about her activities surrounding the 2020 elections”. He characterized her efforts after the election as “minimal and mainstream activity focused on ensuring that reports of fraud and irregularities were investigated”.