The drag on Innogy’s wider retail business could be even greater if the UK government moves ahead with plans to cap standard variable tariffs, it added.
The embattled supplier has been forced to sell its energy at a loss to help fend off competition from a growing number of upstarts entering the market.
The supplier’s troubles stem from the calamitous roll-out of a new IT system in 2013, which triggered a flood of billing errors and complaints as customers fled in their droves.
But following losses in the first quarter Npower was able to claw back 50,000 new customers in the second quarter and slash the number of complaints.
“Of the Big Six energy companies in the United Kingdom, Innogy’s retail brand Npower had the second-lowest rate of customer complaints, whereas it received the highest number of complaints in 2015,” the company said.
Innogy posted adjusted EBIT of about €1.7bn for the first half of the year, up 4pc compared to the same period last year, in large part due to a boom in its German network business.