Britain's energy regulator said Wednesday that household energy bills will rise by 13% from July after global gas prices surged amid the conflict between Iran, the US and Israel.
The annual bill for a typical household on a variable tariff will increase by about £221 ($300), taking average annual costs to roughly £1,862 ($2,500), Ofgem said.
The increase follows sharp rises in global energy markets after shipping through the Strait of Hormuz-a key route for oil and gas exports-was heavily disrupted during the conflict.
Suppliers warned prices could rise further later this year if instability continues.
The new price cap, which limits rates charged to customers on default tariffs, applies to millions of households in England, Scotland and Wales, though households on fixed tariffs will not be immediately affected.
Energy Secretary Ed Miliband described the rise as "deeply unwelcome" and said the government was considering additional support for vulnerable households ahead of winter.
