Natalie Elphicke’s defection to Labour was “naked opportunism, by Labour as much as anything”, Lord David Cameron has said.

Meanwhile, Labour defended its newest recruit, saying the Dover MP had dismissed claims she lobbied ministers to interfere in her ex-husband’s sex offences trial as “nonsense”.

Ms Elphicke quit the Conservatives on Wednesday, hitting out at Rishi Sunak’s “tired and chaotic government” and accusing the Prime Minister of failing to deliver on his promise to “stop the boats”.

Foreign Secretary Lord Cameron criticised his former colleague over the move, telling Sky News’s Sunday Morning With Trevor Phillips programme: “I’m not a fan of defectors. I think it always leaves a legacy of upset and betrayal, and everything else.

“I thought this was just naked opportunism, by Labour as much as anything. This is quite a right-wing Conservative MP suddenly welcomed into the Labour fold having never supported any of their policies, people or approaches.

“The revealing thing is it was like a moment where you look at the Labour Party and think – if you don’t stand for anything, then you’ll fall for stuff like this.”

Ms Elphicke has been accused of asking Sir Robert Buckland, who was the justice secretary and lord chancellor in 2020, to intervene before the hearing of her then-husband Charlie Elphicke’s case.

Labour frontbencher Jonathan Ashworth told Sir Trevor: “She said that is nonsense and not her interpretation of the meeting. I obviously wasn’t in the meeting so I don’t know.

“If this happened at the time, then why did the lord chancellor not raise this issue at the time through his good offices?”

The Sunday Times reported that Ms Elphicke told Sir Robert that it was unfair the case was the first to be heard at Southwark Crown Court after the Covid lockdown and that it was being overseen by Lady Justice Whipple.

One person present viewed her comments as a bid to have the case moved to a lower-profile court to spare her partner public scrutiny, while another saw it as an attempt to replace the senior judge, according to the newspaper.

Sir Robert rejected her plea, suggesting his intervention could undermine the constitutional doctrine of the separation of powers between Parliament and the judiciary.

Ms Elphicke’s former husband Charlie, her predecessor as Dover MP, was convicted of sexually assaulting two women and jailed for two years in 2020.

She ended the marriage after his conviction but supported his unsuccessful appeal, saying Mr Elphicke had been “attractive, and attracted to women” and “an easy target for dirty politics and false allegations”.

Her defection to Labour prompted a backlash among some of its MPs, who raised concerns about the decision to admit her to the party, citing her comments about Mr Elphicke’s case and his victims.

Labour MP for Coventry South Zarah Sultana questioned whether her new colleague’s values were really aligned with the Labour Party’s.

She told the BBC’s Sunday With Laura Kuenssberg programme: “I think it’s great when people are moving towards the Labour movement and the Labour Party.

“Natalie Elphicke, however, is an interesting one because she is a former paid-up member of the ERG (European Research Group), she voted for Liz Truss in the leadership, she’s at odds when it comes to fire-and-rehire, has attacked trade unions and their activities not great on the environment either.

“So unless she’s had the biggest Damascene conversion ever, I just don’t buy it.”

Ms Sultana added: “And it’s concerning as well in terms of conversations I’ve had within the PLP (Parliamentary Labour Party), especially in the Women’s PLP on the comments that she’s made about her ex-husband and the trial.”

Ms Elphicke apologised for the comments supporting her ex-husband following criticism from her new party colleagues.

In a statement on Thursday, she said she condemned “his behaviour towards other women and towards me”, adding it was “right that he was prosecuted” and she was “sorry for the comments that I made about his victims”.