The mother of disgraced former soldier Ben Roberts-Smith has launched an extraordinary character attack on Andrew Hastie, emailing Coalition MPs with accusations that the man who testified in her son’s defamation trial was “not fit” to lead the Liberal party.

An email was sent from Sue Roberts-Smith’s address to at least two dozen Liberal and National MPs containing a 39-page dossier about Hastie early on Wednesday.

It follows the West Australian’s vow to quit the frontbench if the party recommitted to net zero by 2050, which prompted fresh speculation about a future leadership tilt.

In the email, seen by Guardian Australia, Sue Roberts-Smith told MPs that after Jacinta Nampijinpa Price’s sacking from the frontbench “it is time you had a good hard look at Andrew Hastie”.

“He has demonstrated in the articles attached that he is not fit to be the leader of the Liberal Party,” she wrote.

The dossier includes dozens of articles about Roberts-Smith’s alleged war crimes in Afghanistan and the legal battles he waged in a failed attempt to clear his name.

In her email, Sue Roberts-Smith accuses Hastie of doing “everything he can to assist” the two Nine journalists, Nick McKenzie and Chris Masters, who broke the story in 2018 and extensively covered the fallout.

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Hastie, a former captain in the Special Air Service (SAS) who served alongside Roberts-Smith in Afghanistan, was subpoenaed by the newspapers to give evidence after the Victoria Cross recipient launched defamation action against the publications.

In his evidence, Hastie, who was then assistant defence minister, told the federal court it was a “fairly well-established rumour” that Roberts-Smith had kicked an unarmed “PUC” (a “person under control” in military parlance) off a cliff in Afghanistan.

Hastie also told court that there was a “widespread view” within the SAS that Roberts-Smith was a bully and that he was no longer “proud” of a soldier who he once held in high regard.

The court ultimately ruled in the newspapers’ favour, finding that Roberts-Smith had, on the balance of probabilities, committed war crimes in Afghanistan. The high court earlier this month refused Roberts-Smith’s application for leave to appeal against the decision, ending the seven-year legal fight.

Hastie declined to comment on Sue Roberts-Smith’s email when contacted by Guardian Australia.

She was contacted for comment.

The dossier comprised news stories and website references about Hastie dating back to 2010. They relate to a broad mix of topics, including his concerns about China, his own leadership ambitions and decision to abstain from the same-sex marriage vote.

“You should be alarmed at the attachments to this email,” Sue Roberts-Smith wrote.

“The word document has only a fraction of what harm Andrew Hastie has done to the Liberal Party and to others including our family.

The 42-year-old conservative did not run for the Liberal party leadership after the May federal election but has repeatedly spoken of his ambitions to one day fill the role.

Speculation about a future leadership challenge reignited on Monday after Hastie signalled he would quit Sussan Ley’s frontbench if the party recommitted to net zero by 2050, a policy he has described as “moral hypocrisy” and a “scam”.

Ley agreed to review the Liberals’ commitment to net zero by 2050 after winning the leadership, setting up a messy internal fight between supporters and detractors of the target.

On Wednesday, Hastie said most of his colleagues didn’t share his anti-net zero stance as he downplayed suggestions a shift to the backbench could precipitate a leadership challenge.

“Most of my colleagues, in fact, don’t support my position so I’m in the minority here. If you pulled out a spreadsheet … you’d find that a lot of people don’t support my energy position. So I am in the minority here, and I know that,” he said.

Hastie said while he and Ley were not “besties” their relationship was “perfectly fine”.

Ley would not speculate on what would happen to Hastie if he crossed the floor in parliament to support Barnaby Joyce’s bill to dump net zero.

She said: “All of my colleagues are participating in the discussion on energy right now, as they should. And I love it when people have strong views and express them, because they’re coming from the people they’re listening to, from all corners of this country; you get the best possible outcome in decision-making when you harness those ideas and you listen closely.”