British Gas has cut standard electricity prices by an average of 10%.
The energy giant, which supplies electricity to one in four homes, said the reduction for 4.5 million customers came into effect immediately.
The move follows the company's 10% reduction in gas prices, which came into force in February this year.
British Gas, which is part of Centrica, said the total saving for a dual fuel customer at average consumption was around £132.
The average annual dual fuel bill for a British Gas customer is now £1,127, making it the cheapest in the UK for customers who pay by monthly direct debit, the company added.
Managing director Phil Bentley said: "British Gas is offering existing and new customers the cheapest electricity rates in the market place."
British Gas said the recent fall in wholesale electricity prices meant it was able to pass on the cut in tariffs.
Other energy companies - many of which raised prices significantly last year - have come under pressure to cut bills to reflect falling wholesale costs.
These have dropped in line with the cost of oil, which has retreated dramatically from its peak of 147 US dollars a barrel last summer, to around 50 dollars as the global economic crisis deepened.
The company said its electricity prices are now 6% cheaper than at the start of 2007.
