The Big Six energy supplier has today published its financial results for 2015 which saw it make an annual loss of £99m in comparison to a profit of £183m for the previous 12 months.

It also revealed customer account numbers decreased by 7%, from 5.13 million in 2014 to 4.77 million by the end of last year due to “very challenging market conditions”.

This is the latest blow to the energy giant after it was ordered to pay £26m over billing and complaint handling failings which saw it issue over 500,000 late or inaccurate bills.

Last year it was rated the worst energy company in the UK according to a Which? survey which found that the overall satisfaction score was just 35%.

Despite it announcing the loss of 2,400 jobs as part of its two year recovery programme, it said there are “signs of improvement already being seen”.

In 2015, the company halved the rate of domestic complaints received per 100,000 customers, with 50% of this reduction coming in the last quarter alone.

Earlier this year it also announced it would cut the cost of its standard gas price by an average of 5.2% (£32) to take effect from 28 March.

Paul Coffey, CEO of RWE which owns Npower, said: “Npower results continue the trend seen earlier in 2015, but they are nonetheless extremely disappointing and we are starting a two year process to fix them. They show a business that tried to do too much, too soon while not focusing enough on the fundamentals in a constantly changing market.

“Our plan is to create an Npower that delivers better service, is more attractive to customers and better prepared for future opportunities – all at lower costs. This will be a huge task for all of us but we are determined to create the better business that our customers expect and shareholders demand.”