The short-lived PM will use a speech at the Institute for Government to defend tenure and explain her time in charge, nearly a year on from the ill-fated mini-budget that helped end her premiership.
According to The Daily Telegraph, Ms Truss will point out that under her plans £18.4billion would have been saved in 2023/24, with another £17.1billion in 2024/25.
“What I sought to do was change the trajectory of spending by holding spending down and not allowing any new spending to take place over the coming spending review period,” the paper reports she will say.
“Not reopening the spending review represented a tough approach on spending, given the levels of inflation.”
That decision, she will say, would have saved £13.6billion in 2023/24 and £12.3billion in 2024/25 compared to Mr Sunak’s public spending plans.
Plans to increase benefits in line with wages, not inflation, would also have saved £9.6billion over two years.
“Compared to what we are spending now, we would have saved £18.4billion in 2023-24 and £17.1billion in 2024-25,” she will say.
She will add: “Even those modest savings did not command the support of the parliamentary party.
“It is a very serious issue for those of us who want to see smaller government that currently making significant changes to spending simply doesn’t have enough political support.”
It is the latest public intervention from the former Conservative leader, who defeated Mr Sunak in last summer’s Tory leadership race before resigning in October.