The price cap is set every three months. Domestic energy bills fell by 7% between April and July, following a shake-up in charges by the government.
That change was announced just before the outbreak of the conflict in Iran. However the cap from July to September will reflect the 25% increase in the global price of gas caused by the war, particularly the effective closure of the Strait of Hormuz.
The wholesale price, paid by suppliers, makes up about 40% of a household gas and electricity bill. Some energy suppliers have forecast that energy prices could move even higher by the autumn and winter.
The government has said it is working on plans to provide targeted support for those most in need before bills become even more expensive into the winter, when households use more energy.
A typical household is already paying about £600 a year more than before the price shock of 2022-23. Billions of pounds is owed to suppliers in unpaid bills, and many people with disabilities have high energy use throughout the year to run specialist equipment.