The boss of energy giant Npower has said his bonus will be slashed because of the company's poor customer service.

Paul Massara, chief executive of Npower, told ITV's Daybreak that his firm had not delivered a good level of service that "customers deserve".

"When the board sit down and review my bonus they will reduce my bonus because I haven't actually delivered for customers," Massara explained.

He added: "I think we are concerned for all customers who care. We care about how they are impacted every single day."

The announcement follows research released by Consumer Futures, which revealed the energy firm is the most complained-about in the UK.

The data found Npower received triple the amount of complaints than its closest rival in the second quarter of 2013 - representing 202 complaints per 100,000 customers between April and June this year.

"We've had some challenges with a new computer system and we're sorry that this has caused problems for customers," said Roger Hattam, director domestic retail business at npower, while also admitting that some customers "have not had the service they deserve".

"I want to reassure them that we're working very hard and making progress in ensuring that these issues are resolved as quickly as possible."

EDF, France's state-controlled energy group, came in second with 72 complaints for the same customer sample size, during the same period.

E.ON ranked third with 60, British Gas came in fourth with 55, while Scottish Power was fifth with 41.

"Energy companies have repeatedly said they want to rebuild consumer trust," said Audrey Gallacher, director of energy at Consumer Focus.

"Good customer service and complaints handling are key ingredients to achieving this and suppliers still have a long way to go."

The data comprises complaints received by Consumer Futures as well as those made to Citizens Advice and the energy ombudsman.

The latest data shows that complaints about the big energy firms have steadily climbed from October 2012.

"People are being hit with large back bills, find their bill unclear and direct debit customers are frustrated companies are holding onto their money when they're in credit," said Citizens Advice's chief executive Gillian Guy.

"Energy companies need to put customers first and be much more transparent about where they make their profits."

Npower, which is owned by German company RWE, recently announced 1,460 job losses across some of its UK sites.