German-owned utilities company lost 351,000 customers and £106m in 2015Reuters

The UK's second largest trade union is urging Npower bosses to hold crunch talks after the energy giant announced it would axe 2,400 jobs.

Unison warned the firms' management could "compound the anxiety" of Npower staff if they did not meet union representatives to discuss the cost-cutting exercise.

"We're calling for an emergency meeting so we can work jointly on finding a way out of the mess the company currently finds itself in," said Dave Prentis, the general secretary of Unison. "The workforce will be hoping that the worst is now behind Npower, and that in future employees are the first to know if jobs are under threat."

The comments come after Npower, which is owned by German unities company RWE, unveiled a two-year recovery plan in reaction to losing 351,000 customers and £106m ($227m) in 2015.

"The main reason for this is serious process and system-related problems in customer billing," RWE said in a statement.

"Substantial earnings shortfalls also stemmed from the fact that residential and commercial customers switched providers or we were only able to retain such customers by offering them contracts with more favourable conditions.

"In addition, there is an increasing trend towards saving energy, which also hit us harder than expected."

£26m settlement with Ofgem

Npower now plans to cut 20% of its 11,500 UK workforce, with a mixture of employees and contractors expected to lose their jobs. The company was forced to pay a £26m customer redress settlement in December after a probe from energy watchdog Ofgem.

The regulator said Npower's billing issues affected more than 500,000 of its customers between September 2013 and December 2014.

Dermot Nolan, chief executive of Ofgem, said: "Npower failed its customers. Not only have its billing and complaint handling procedures been chaotic, it treated many of its customers poorly, which is completely unacceptable.

"Npower's management failed to act quickly enough to protect its customers when things went wrong with changes to its IT system."

The company has now promised to put in place a "number of key measures" to improve its billing. "A major set of improvements was made to the billing system last month," Npower said.

"Steps are being taken to make it easier for advisers to serve customers well, for example, by reducing the numbers of different screens they need to use.

"Key service processes are also being overhauled, including the home move process. Taken together, these will lead in time to a significantly improved customer experience with fewer."