Former foreign minister Julie Bishop has delivered a veiled insult to Scott Morrison at a Senate inquiry, admitting she would not have left politics if there had not been a leadership change.

“When Mr Turnbull was prime minister, I was not planning to retire from the cabinet,” she told the inquiry on Thursday.

Ms Bishop and former defence minister Christopher Pyne were grilled at an inquiry into post-ministerial employment on Thursday that is considering whether the rules should be tightened.

Her relationship with Mr Morrison is notoriously cool – she famously turned on her heels and left the parliamentary chamber after he rose to speak about her retirement, later suggesting she was running late for a flight.

Despite the Mr Pyne and Ms Bishop being cleared of any breach of the rules by an inquiry led by the head of the Department of Prime Minister and Cabinet, the Senate voted to establish a parliamentary probe into jobs for ex-MPs.

The decision of former defence minister Mr Pyne to take a job with consultants EY advising defence business, and the former foreign affairs minister’s job with Palladium has triggered uproar in Parliament over claims ministerial standards have been breached.

Both Mr Pyne and Ms Bishop told the inquiry that the requirements were voluntary and not legally binding.

The former cabinet ministers also confirmed they had had no conversations with current or former PMs about how the rules would work when they decided to leave politics.

“There was no exit interview were that was made clear, no,” Mr Pyne said.

Ms Bishop, appearing via teleconference while the committee met in Canberra, said the onus of abiding by the rules that prevent former ministers lobbying governments or public servants should fall on those still in parliament.

“You could amend the guidelines as to make that explicit what would be required should a serving minister ever find themselves in that position,” she said

Ms Bishop also told the hearings she was “not aware of the penalty that would apply if there were a breach” of the ministerial standards.

But Queensland Senator Larissa Walters said the rules were a joke.

“Julie Bishop just confirmed to me in the Senate Inquiry that the Prime Minister never once asked about her complying with the ministerial standards in relation to her post-parliament employment. These weak standards are so obviously not enforced. What a joke,” she said.

South Australian senator Rex Patrick said the new jobs for the ex-MPs don’t pass the pub test.

“Of course they’re allowed to take jobs, but not going from defence minister to defence consultant – that is a bridge too far,” he told Sky News.

“He can’t un-know what he knows … that is an advantage EY gets that other companies don’t get. If this doesn’t breach the bar for breach of ministerial standards, then nothing does.