Labour has questioned who will pay for Liz Truss’s economic plans in advance of this week’s energy package and mini-budget while criticising the Tories’ record on growth in a sign of how they plan to attack the government over the state of the economy. As Truss and her chancellor, Kwasi Kwarteng, prepare to present their plans, Pat McFadden, the shadow chief secretary to the Treasury, highlighted the difference between Labour’s proposals to fund an energy price freeze with a windfall tax on oil and gas companies and the Conservatives’ unfunded plans. He said under the Tory proposals, which will probably be paid for by borrowing, “working people will be left paying the bill for years to come” and the “fundamental question which remains unanswered on this is who pays, and what do you get for it?” Labour’s criticism of the government’s uncosted plans marks a return to political debate after 10 days of national mourning for the Queen. Politics will largely go back to normal this week with a packed schedule for the prime minister. She has diplomatic meetings in New York before more details of her energy package are outlined on Wednesday and the mini-budget is held on Friday, which is expected to contain the cancellation of the national insurance rise. Truss and Kwarteng are keen to frame their plans as a move towards promoting growth at all costs. But McFadden questioned the Conservatives’ record on growth and claimed the party is out of ideas after 12 years in power. “It’s just another zigzag in the record of low growth over which they have presided,” he said, adding that the government’s “record on economic growth has been a failure”. Labour first proposed an energy price freeze over the summer, with a windfall tax to pay for it. Truss has followed suit by backing an energy price freeze but rejected the idea of a windfall tax and has not released details of how it will be paid for. “Even the energy companies themselves accept the need for a windfall tax,” McFadden said. “But instead the government is insisting that the costs must all go on borrowing. This creates a fundamental difference in who should pay for the policy and in how long these costs must be paid into the future.” At the mini-budget, Kwarteng is also expected to reverse the national insurance rise, which Labour opposed when it was brought in last year by Boris Johnson and Rishi Sunak. Kwarteng also plans to freeze corporation tax, which Labour said was “a return to the failed policy pursued by George Osborne a few years ago”, and introduce low-tax “enterprise zones” which the opposition said was an “even older idea, tried as far back as the 1980s”. Meanwhile, new analysis by the Institute for Fiscal Studies (IFS) found on Monday that the lowest-paid workers stand to gain just 63p a month while the richest could get back £150 a month from the reversal of the national insurance rise. The IFS has produced data suggesting the full reversal of the rise is likely to benefit most those who are paid more than £100,000, and will barely help the poorest 3m households. Those in households with the average UK household income of £31,400 will save about £20 a month, while households with an income of £55,000 will save about £58 a month, according to the IFS analysis. Kwarteng could also announce further tax cuts such as a future reduction in income tax by 1p or even 2p. He is expected to present his plans without any independent analysis of how this will affect the national finances or how it will be paid for.