Added together, the large suppliers now have 92.4% of the market, down from 99.8% five years ago.
In other words, independent suppliers have increased their share from just 0.2% to 7.6% over the same period.
The largest independent has grown ten-fold in just three years, and now has more than a million customer accounts.
Many of the smaller firms claim to offer cheaper bills than the big six suppliers.
If the trend continues, it may reduce pressure on the competition authorities to shake up the energy market.
The Competition and Markets Authority (CMA) began an enquiry into the big six suppliers earlier this summer, after the regulator, Ofgem, said the market was not working in consumers’ best interests.
‘Two million’ customers
The latest figures, from independent research group Cornwall Energy, show that customers have 3.8m accounts with the smaller suppliers, and 45.9m with the big six.
The figures relate to the third quarter of 2014.
The largest independent, First Utility, has grown ten-fold in just three years, and now has more than 550,000 customers.
Taking into account both gas and electricity, those customers have 1.02m accounts between them.
The next biggest independent supplier, Utility Warehouse, has 835,000 accounts.
The Department of Energy boasts that the total number of suppliers has “almost trebled” to more than a dozen since 2010.
“With over two million customers now signed up to independent suppliers overall it’s clear that households increasingly trust them and are benefitting from competition in the market,” said energy minister Ed Davey.
However consumer bodies argue that more should be done to increase competition further, to break the “stranglehold” of the big six firms.
The CMA enquiry will look at the possibility of breaking up the big suppliers, all of whom also generate electricity.
It is due to report at the end of 2015.