Paul Johnson, director of the Institute for Fiscal Studies (IFS) think tank, said Truss and Kwarteng's tax cuts could be the largest since 1988, and risked putting Britain's public debt on an unsustainable path.
The IFS, together with U.S. bank Citi, estimate household energy subsidies will cost about 120 billion pounds over two years, while six months of business energy subsidies will cost 40 billion pounds.
read moreThese are a one-off, and the bigger concern for the IFS is around 30 billion pounds of permanent tax cuts - starting with 14 billion pounds in reduced payroll taxes, confirmed on Thursday, and 15 billion pounds of cuts to corporation tax.
For Kwarteng, tax cuts and deregulation are a way to end what he calls "a cycle of stagnation" that led to tax rates being on course for their highest level since the 1940s.
"We will liberalise planning rules in specified agreed sites, releasing land and accelerating development," Kwarteng is expected to say.