British Gas warns customers they must take action before 9pm on Tuesday night

British Gas - a major UK energy firm with seven million customers - is offering thousands half price electricity this evening. British Gas customers can get the discounted energy between 9pm and 11pm tonight, the supplier has confirmed.

It's part of the suppliers popular Peak Save scheme which usually rewards customers for shifting their usage to off-peak times. Tonight's offer is known as a Green Flex event, which rewards customers who opt in, with half price electricity when there's surplus renewable energy available in the grid.

British Gas said it has emailed customers eligible to take part, and you will need to click a link and opt in to do so. They’re short, one or two-hour events where you can get your electricity for half price. You can be on any tariff to take part. And by moving your electricity use to when there’s likely to be lots of renewable energy around, you’re saving money and helping the planet.

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British Gas explains: "Green Flex events take place at certain times, depending on how sunny or windy it gets in the UK. Already a PeakSaver? Then you’re all set. If not, register for PeakSave and we’ll let you know when everything’s up and running.

"We’ll email you if there’s an event coming up, either on the day or the day before. You’ll need to opt in to take part. Power up with half-price electricity. So, think dishwasher, washing machine, or vacuum cleaner. Tumble dryer? Even better!

"Your smart meter will tell us how much you used, and we'll work out your credit." It adds: "After each event, we’ll credit half of what you spent back to your account and the payment will show up as ‘PeakSave Green Flex Credit’ on your next bill or online statement.

"It’ll normally appear within two weeks of each event ending."