Energy firms have hiked prices at a rate of more than one a week this year – adding £840million to household bills, according to research.
Thirty suppliers have announced 43 increases in their standard variable tariffs since the start of 2018.
It means some companies have upped their prices twice this year.
More than 12 million households have seen their annual gas and electricity bill jump by an average of 7% – or £70 a year – as a result, according to a report from price comparison website uSwitch .
It calculated that the combination of the 43 increases by the 30 firms would see them rake in £840million in additional revenue.
Suppliers say they have been forced to increase bills because of a sharp rise in wholesale gas and electricity costs.
However, the hikes come ahead of rules to cap rip-off standard variable tariffs, expected later this year.
Industry giant British Gas is due to increase its standard tariff by an average of 3.8% on October 1 – its second in five months.
The two combined will add £104 to the average annual bill for 3.5 million affected customers.
Yet the hike was announced just a week after the firm revealed a £430million profit for the first six months of this year.
According to uSwitch, there are large variations between what different customers with the same supplier pay around the country.
For example, a British Gas customer in the Midlands will see their bill rise by £119 a year on average, compared to £84 for someone in North West England, uSwitch found.
Suppliers say it is because of the different costs of getting energy around the country.
Rik Smith, uSwitch.com energy expert, says: “Many households have refused to take this lying down.
“Over three million have switched supplier already this year and saved up to £482 in the process.
“With no end in sight to increases in the cost of gas and electricity, now is the time to secure a better deal – wherever you live.”