Liz Truss made the astonishing claim that the Tories would have done better at the election had she continued as the party's leader after the mini-budget.
The prediction came during a Tory conference fringe event this lunchtime, her only set-piece appearance.
In a packed room of over 300 loyal supporters, Ms Truss argued she would have led the party to a better election outcome in July had she not quit.
However when asked if she could have won a majority, she demurred and said it would always have been a tough election.
The 49-day premier said that Boris Johnson could have won the election for the Tories, and her party's big “stupid move” was getting rid of him in the first place.
She also leveled an attack at Theresa May, who last week wrote an article criticizing Ms Truss's time in office as one of the reasons they lost the election.
This weekend, Mrs May wrote: “Our reputation for economic competence was shattered by the budget of September 2022”.
Asked how she'd respond, Ms Truss laughed, shrugged her shoulders and hit back: “I don't know what to say about the 2017 election, and our policies on social care!”
“I'm not going to indulge in a slanging match with Theresa May.”
Shortly after she continued her slanging match against Theresa May, accusing her of being “part of the establishment”.
She warned that many Tories still wrongly believe that the great political divide in politics is along traditional right-left lines, while in reality it is now “between the establishment and those who want radical change in our country”.
Liz Truss also refused to endorse any of the four candidates for Tory leader, accusing them of refusing to talk about many of the biggest crises facing Britain.
Among those that she cited as being the most important thing they should be debated include backing fracking, scrapping the Human Rights Act, reversing the equality act, and scrapping Tony Blair's constitutional changes to the judiciary and Supreme Court.
She added: “They think 'all we need to do is show competence and we will be ushered back into office'.”
“They have to explain what went wrong, why things are so bad for the Conservatives and what they're actually going to do.”
Opening the event, she blasted the legacy of the past 14 years of Tory government, accusing them of failing to roll back the socialist policies of Tony Blair and Gordon Brown.
She argued Sir Keir Starmer is making things worse, but Britain was already a socialist country by the time they won the election.
She fumed: “A lot of the problems we are facing now are as a result of us failing to turn things around.”
Asked if she may return to Parliament, she refused to rule it out, but said she is enjoying her new life in the private sector and is off to a Conservative conference in Australia later this week.