More than one in five households are now being supplied by small and medium sized energy firms.
That has moved the Big Six suppliers’ combined market share to a record low of 79% for electricity and 78% for gas – down from 84% for both gas and electricity at the end of 2016.
Ofgem’s latest statistics reveal around 5.1 million electricity consumers and 4.1 million gas consumers have switched suppliers in total.
More than a third of these consumers moved from one of the Big Six firms to rival companies, a record high.
Last December, small and medium sized firms were supplying 21% of consumers for electricity and 22% for gas.
Dermot Nolan, Chief Executive of Ofgem said: “The largest suppliers are under pressure as more consumers switch away to small and medium sized suppliers. With more customers voting with their feet, the message is clear: suppliers need to look at what they are offering to their customers or risk losing them.”