Former prime minister Rishi Sunak accused the government of "fiddling the figures" and of "not being straight with the British people".
Delivering the Conservative Party's formal response to Labour's budget, it was Mr Sunak's last act as interim leader of the Conservatives.
"Time and again we Conservatives warned that Labour would tax, borrow and spend far beyond what they were telling the country, and time and again they denied they had such plans," he said.