This brings the total customer loss in Britain to 238,000 in the first half of 2019, less than the 400,000 at rival E.ON SE, which will be the future owner of Innogy's British retail activities as part of an asset swap with its parent RWE AG.
E.ON is still turning an operating profit in Britain, where a cap on power tariffs has been a major headache for local energy suppliers, it said earlier this week, adding it still saw potential in the market going forward.
In contrast, Innogy's British subsidiary npower, one of the country's so-called "big six" energy providers, widened its operating loss to 81 million euros (£75 million) in the first half, from a loss of 18 million in the same period last year.
"The market situation in the retail business remains highly competitive," Innogy said in a statement. "In the company's UK retail business... the persistently difficult market environment resulted in a further decline in customer numbers."
The group still confirmed its full-year profit outlook, still expecting adjusted earnings before interest and tax of about 2.3 billion euros and adjusted net income of about 850 million.
(Reporting by Christoph Steitz; Editing by Riham Alkousaa and Rashmi Aich)