The "big six" energy firm blamed the hike on the increased costs of supplying electricity and defended the move, claiming it had shielded customers from rises since November 2013, but could no longer offset the cost.
Centrica's chief executive, Ian Conn, who received a 40 per cent pay rise in 2016 taking the total to £4.15 million, recently hinted price rises were on the way and suggested the company's costs have risen.
"Instead of pointing the finger at policy costs - which have been shown to cut overall bills by reducing waste - British Gas should be looking to the long term and backing low-priced renewables and smart, flexible technology which have been reported time and time again as offering billions of pounds of benefits to United Kingdom homes and businesses", he said.
It's half year results also revealed a loss of more than 377,000 United Kingdom customer accounts in the first half of 2017.
"This is a colossal increase that will really hurt customers already struggling with rising prices due to the deteriorating economic situation".
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Mark Hodges, chief executive of Centrica Consumer - the parent company of British Gas - says: "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 hard decision to have to announce an increase in electricity prices".
"So let this be a clarion call for British Gas customers (and all those on big 6 standard tariffs)". Three million Brits are going to pay 76 pounds a year more than they are now when you have acknowledged that there is no increase in the wholesale price of electricity.
The Conservative manifesto pledged a wide-ranging cap to protect 17 million customers from excessive rises, saving people an estimated £100 a year.
Stephen Murray, energy expert, MoneySuperMarket added: "This announcement from British Gas must be one of the worst kept secrets in the history of the energy industry".
In the run up to the June General Election, the Conservatives promised and energy price cap, in a supposed departure from traditional Tory liberal economics which rejects state interference in the market.
"For example, British Gas managed to lose 377,000 United Kingdom customers in the first half of the year, despite waiting until after its rivals had increased prices before following suit". "We want to see rapid progress on this commitment".