A London energy company has been crowned the UK’s fast-growing company.

Bulb topped the annual 100 list published by online investment platform SyndicateRoom, having signed up more than 870,000 households across the UK from just 85,000 a year ago.

Bulb aims to keep energy switching simple, cheap and green despite rising prices across the industry by using software to offer its members a single tariff.

Set up in 2015 by friends Hayden Wood and Amit Gudka, 100 per cent of the company's electricity is renewable – taken from independent energy generators across the UK – while ten per cent of its gas is renewable.

"Both Amit and I used to work in the energy industry," Wood told SyndicateRoom.

"We were the only ones that had corporate jobs amongst our friends, so whenever we would go to the pub or to parties, we’d always be in the corner talking about work.

"We saw first-hand how the energy market was broken. It was the same story at all the big providers – poor service, high tariffs, inefficiency and little effort being made to champion renewables."

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Rather than relying on traditional advertising efforts, Bulb's popularity has flourished through social media, word of mouth and its referral programme.

The firm has raised £60 million in growth funding and has big targets.

"Our ambition is to add another million members to Bulb in 2019," added Wood. "This is really challenging – no energy supplier has grown at that rate before.

"It'll be hard, but that’s our ambition. We also want to increase our investment in new technology. For 2019, we're really excited about what we can do with smart meters."

Wood said Bulb's early-stage investment came from savings, friends and family before large-scale investors DST Global and JamJar Investments came on board.

"We were looking to raise quite a lot of money for a start-up – £1.3 million. Starting an energy company, by definition, is an expensive thing to do," he said. "There are many regulatory steps you need to complete before you can start providing electricity and gas.

"We couldn't take the typical start-up route of raising a small amount of money and then raising another round once we’d proved things were working.

"It was quite challenging, but we were fortunate in that we knew or had worked with many of our early-stage investors. This did make things easier – it gave them the confidence to invest."