Electricity bills are set to increase by 12.5 per cent with the higher prices set to come in on September 15, just as temperatures begin to drop.
The Big Six energy giant confirmed the price rise after a blunder on Monday saw the group mistakenly publish an incomplete statement about increasing electricity tariffs on its website.Related articles
GETTY•PABritish Gas electricity price increases will affect millions of Britons
The average annual dual-fuel bill for a typical household on a standard tariff will rise by £76 to £1,120, a 7.3 per cent increase.
However, gas prices will be held at their current level.
Centrica-owned British Gas said the price rise is its first since November 2013 and the group pledged to help protect more than 200,000 vulnerable customers from the increase.
Centrica Consumer chief executive Mark Hodges said: "We held off increasing prices for many months longer than most suppliers in order to protect our customers from rising costs, so it is a difficult decision to have to announce an increase in electricity prices.
GETTYBritish Gas is the biggest energy supplier in the country
"This rise reflects an underlying increase in policy and transmission costs."
Centrica chief executive Iain Conn told the BBC's Today programme that they were "selling electricity at a loss and that is not sustainable".
He added: "Our electricity prices have been the same since 2014. Since then we have seen significant pressures on cost in two areas - the transmission and distribution of electricity to the home and secondly government policy costs which are recouped through the bill."
Before the General Election, Theresa May announced plans for a cap on standard variable tariffs (SVT) which could have saved millions of people around £100 a year.