Political pundits often talk about the “transactional costs” of coups. On Thursday, the cost of having around a deeply unhappy and still angry ousted leader suddenly became alarmingly high for the government.

When Malcolm Turnbull told parliament that the prime ministerial office of Tony Abbott knew of the 2015 deal with Senate crossbencher David Leyonhjelm to attach a sunset clause to the import ban on a particular Adler shotgun, it turned the already bitter relationship between the current and former leaders into a potential crisis.

Abbott had denied any deal by him or his office. Now – in parliament – he was in effect being called a liar by the man who supplanted him. It doesn’t come much more serious than that.

The Adler seven-shot lever-action shotgun, advertised as “a game changer for the Australian market”, had changed the game in their mutual hostilities.

To say Turnbull has had yet another bad week doesn’t tell half of it. It’s been little short of disastrous and there will be more fallout.

It started on Tuesday when Turnbull on the ABC did not immediately rule out Leyonhjelm’s call to put the Adler import ban on the table in the negotiations about the government’s industrial relations legislation. Leyonhjelm felt “dudded” because the ban had been extended despite the sunset deal.

Abbott decided to inject himself into the debate, with a tweet saying in part “Disturbing to see reports of horse-trading on gun laws”, while his former chief-of-staff Peta Credlin on Sky said “there was absolutely no deal between Tony Abbott and David Leyonhjelm in order to bring in the Adler shotgun”.

On Wednesday Abbott raised the stakes, with comment to reporters and then a rare appearance on the ABC’s 7.30, where he displaced Foreign Minister Julie Bishop who had been due to be the guest on the show. She was less than happy at being bumped in favour of Abbott but the program knew a better political story when it saw it.

Abbott, who regards Bishop as having been disloyal to him, would have been grimly pleased at one-upping her if he’d known.

Pressed by Leigh Sales on the sunset clause deal, Abbott said: “No deals from me. No deals from my office. No deal.”

He dismissed the August 2015 email from Justice Minister Michael Keenan’s office to Leyonhjelm’s office – confirming Keenan and Immigration Minister Peter Dutton had agreed to insert a sunset clause in the August 7 prohibition in return for Leyonhjelm co-operating on migration legislation – as probably staffers just “telling the good senator what was happening anyway as a matter of course, in an attempt to get him to support something that we thought was a very good idea”.

On Thursday morning Keenan and Dutton met Turnbull. Keenan had a paper trail between his office and the Abbott prime ministerial office relating to the deal.

It was decided Abbott should be given the opportunity to clear things up. Dutton went to see him. After the Dutton-Abbott discussion, Turnbull expected Abbott to put out a statement before Question Time. It didn’t come.

Turnbull knew he and the ministers faced imminent cross-examination from Labor in the House. They couldn’t lie to parliament – a hanging offence – and, anyway, the paper trail would eventually come out.

In Question Time Dutton and Keenan both indicated the Abbott office had been in the loop. Turnbull then delivered the coup de grace. He had made inquiries, he said, and “I’m satisfied that the minister for justice acted in the full knowledge of the prime minister’s office at that time”.

After Question Time Abbott made a personal explanation. He said the suggestion Labor had put to parliament that he “had somehow connived at a deal with senator Leyonhjelm to weaken Australia’s tough, gold standard gun control laws” was “absolutely and utterly false”.

He did not refer to the headline story – that Turnbull had just accused him of being privy to the Leyonhjelm deal.

Abbott went on to give the background – citing a July 2015 note from an adviser – to his government imposing a “temporary ban” on the import of the guns until there had been a review and updating of the regulations.

He asked rhetorically: “How can there have been some kind of deal, or concession, or weakening for senator Leyonhjelm on 11 or 12 August if the temporary ban was what the government had always intended, pending a permanent resolution of this by COAG?”

Presumably the documentation will come out sooner rather than later. Beyond that, it’s uncertain where things will go from here.

Both Abbott and Turnbull will be at the weekend NSW Liberal meeting which is to consider reform of the state division of the party, something Abbott has made a personal cause.

Given this week, such proximity is awkward timing.