Craig Mackinlay, the Tory MP and chairman of the Net Zero Scrutiny Group, told The Telegraph it was a “problem” that “the loan scheme is reliant on energy prices coming down in future”.

He said: “If they don’t come down, you’ll face a little bit of a discount this year, but then the full charge plus a £40 charge in future years. We could be in exactly the same position next year and the year after until we solve the underlying problems of our energy policy with various quasi-socialist proposals.”

Rachel Reeves, the Labour shadow chancellor, also accused the Government of “gambling” that wholesale prices will fall.

Chris Bryant, another Labour MP, said that the £200 energy rebate “is actually a loan which will put bills up an extra £40 every year”, adding: “It’s bad enough bribing voters with their own money, but lending people money and pretending it’s a grant is dishonest.”

Mr Sunak denied that his high-tax, high-spend policies were “unconservative” or “Labour-lite”, saying: “For me, being a Conservative, part of that is about being responsible with people’s money and being responsible with the public finances.”

The interest rate rise will see monthly bills jump immediately for households on standard variable and tracker-rate mortgages in the first back-to-back increase in the cost of borrowing since 2004.