About 8.5 million households are currently on fixed-priced energy deals with one of the 10 largest suppliers, according to Ofgem. They will see the biggest increase in costs once their deals end. Last August, the cheapest fixed tariffs cost £1,116, according to comparison website Uswitch. These customers will see bills jump by £855, or £71 a month.

Households that took out a fixed tariff as the energy crisis began to unfold in late 2021 will be insulated for most of this year. However, they will see a large spike in bills at the end of 2022. The 10 cheapest deals cost £1,266 on average in October. If the price cap rises as forecast this winter, these customers face paying an extra £974 a year once their contracts end.

The Government will offer grants of up to £350 to 28 million households as a way to ease the pressure. The discount will be recovered from bills, which will be £40 more expensive each year for the next five years, when, the Government hopes, gas prices will be lower.

Ms Wild added: “Measures announced by the government today will go some way to provide relief to all households, but they don’t go far enough. Energy rebates are a buy-now-pay-later solution which only provide temporary relief later this year.”

Traditionally, the solution to rising prices has been to shop around for a better deal. But the energy crisis has caused small suppliers to collapse and those that remain to pull their best offers. The average fixed deal now costs £2,492 over a year, according to Uswitch. This is more than the price cap, which only applies to a supplier’s default, or standard variable, tariff.

The 10 cheapest contracts cost an average of £2,259 per year, while the cheapest deal, from SSE, costs £2,050. Some energy firms are offering fixed deals costing up to £4,200.