British gas and electricity supplier Npower says it is cutting 2,400 jobs, a fifth of its workforce, after losing hundreds of thousands of customers and reporting poor financial results.

The company, which is owned by German group RWE, said Tuesday that the cuts to its 11,500-strong workforce would hit both directly employed and contract staff.

Npower has seen its share of Britain's competitive domestic energy market crumble amid rising customer dissatisfaction. In December it was fined 26 million pounds ($37 million) by the U.K. energy regulator for providing poor service to customers.

Chief Executive Paul Coffey said the company was starting a two-year process to reverse "extremely disappointing" results.

Dave Prentis of the Unison union said workers were paying the price for "poor decision-making at the very top."