Natalie Elphicke, the new Labour MP for Dover, has been accused of lobbying ministers over her then-husband Charlie's sexual assault case.
Ms Elphicke is accused of asking Sir Robert Buckland, the then justice secretary, to help move the date of the case, apparently to avoid publicity.
A spokesman for Ms Elphicke, who defected from the Conservatives last week, said the claims were "nonsense".
Labour questioned why they were not raised earlier.
Sir Robert told the Sunday Times: "She was told in no uncertain terms that it would have been completely inappropriate to speak to the judge about the trial at all."
The OceanNewsUK has confirmed Sir Robert's account with him.
Labour MP Jonathan Ashworth questioned the timing of the accusations on the OceanNewsUK's Sunday With Laura Kuenssberg programme.
"I don't understand why the Lord Chancellor at the time did not raise this and why he's raised it now," Mr Ashworth said.
Foreign Secretary Lord Cameron was also asked about Ms Elphicke on the programme.
He said he had not examined the story closely, but was of the opinion that the fact that Labour welcomed in a person with little affiliation for the party spoke volumes about party.
"All I know is that Natalie Elphicke's defection said a little bit about Natalie Elphicke, but I think it said rather a lot more about the Labour Party," he said.
Charlie Elphicke's trial was due to be one of the first cases after Covid restrictions were lifted in courts which, potentially, could have meant a greater focus on the case.
He was jailed in 2020 at Southwark Crown Court for two years for sexually assaulting two women.
Ms Elphicke replaced her ex-husband as MP for Dover after he was charged, and announced that their marriage was ending after he was convicted.
Ms Elphicke and four other Conservative MPs were also found to have breached parliament's code of conduct by attempting to influence legal proceedings.
They had written to senior members of the judiciary raising concerns that a more junior judge was considering publishing character references provided for Ms Elphicke's husband.
At the time, Labour's shadow leader of the Commons, Thangam Debbonaire, said the incident showed the Conservatives "think it is one rule for them and another for everyone else".
Ms Elphicke surprised Westminster last week when she defected from the Conservatives to Labour.
She had been seen as being on the right of the Conservative Party - and her being welcomed into Labour has been criticised by some.
Labour MP Zarah Sultana told Laura Kuenssberg's show that she had questions about Ms Elphicke's defection.
"Unless she has had the biggest Damascene conversion ever, I just don't buy it," Ms Sultana said.
Ms Elphicke apologised on Thursday after an interview re-emerged, in which she said her ex-husband was "an easy target" for false allegations because he was "attractive".
Responding to the latest allegations, a spokesman for Natalie Elphicke said: "This is nonsense. It's certainly true that Mr Elphicke continued to be supported after his imprisonment by a large number of Conservative MPs who had known him for a long time, including some who visited him and independently lobbied on his behalf, which was nothing to do with Natalie."
A Labour Party spokesman had said: "Natalie Elphicke totally rejects that characterisation of the meeting.
"If Robert Buckland had any genuine concerns about the meeting, then he should have raised them at the time, rather than making claims to the newspapers now Natalie has chosen to join the Labour Party."
