As more and more consumers switch their gas and electricity suppliers, EDF have lost 266,000 UK customer accounts.
The French-owned company suffered a great deal of their losses at the start of the year, but has since begun to arrest the slide.
EDF currently still has 5.4 million UK customers.
Ofgem said that 1.1 million gas and 1.4 million electricity customers switched between January and May with 4% moving to independent suppliers.
British gas owner Centrica remains the biggest energy provider with 27.9 million customer accounts and said that it plans to cut 6,000 jobs.
EDF has not commented on whether or not it plans to cut its prices in the wake of a 5% reduction by British Gas.
A spokesman for EDF said: "Our prices are under constant review and we work to ensure that our tariffs attract new customers and offer good value to existing ones.
"EDF Energy's standard dual fuel prices have been the cheapest of the major suppliers for the majority of the last three years."
The company said that UK profits before interest were flat at €1.3bn (£911m) and were held back by lower electricity market prices but supported by greater cost control.
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