Growing numbers of dual fuel customers are now with an independent provider rather than one of the Big Six, according to an energy markets consultancy.
Around one in six (17.4%) dual fuel customers across Britain who get their gas and electricity from the same provider are with an independent supplier, consultancy Cornwall Energy found.
It said this marks an increase from the one in eight (12.6%) dual fuel customers who were with independent providers in 2015.
In the last year alone, 2.2 million accounts on any type of tariff were switched to independent suppliers, the research found.
Robert Buckley, director of Cornwall Energy, said: "This data shows one of the biggest shifts to independents in the past 12 months."
The analysis found around one in four non-Big Six dual fuel accounts are held with challenger brand First Utility.
The brands known as the Big Six are British Gas, Npower, EDF, Scottish Power, SSE and E.ON.
Consumer group Which? said last week that the gap between average Big Six energy tariffs and the cheapest deals on the market has increased significantly since the competition watchdog started an investigation into the sector,
The Competition and Markets Authority (CMA) is due to release the final report of its two-year investigation into the energy market later this month.
But Energy UK, which represents the industry, disputed the Which? findings, saying energy companies are consistently bringing down their prices every day.
A Department of Energy and Climate Change spokeswoman said: "The power is in your hands to compare, switch and save today.
"We've made it easier than ever before to find the best deal on the market. There are now more than 40 suppliers to choose from, meaning more competition and better offers for consumers."