WORCESTER based energy giant npower has lost 300,000 customers in just one year, it has emerged.

The firm, which is based in Warndon just off the Sixways roundabout, has also seen its profits fall by two thirds in the first half of this year.

The company has repeatedly come out on top in surveys of the amounts of complaints made to the big six energy suppliers – npower, British Gas, SSE, EDF Energy, E.ON and Scottish Power – and a revamp of its computer systems 18 months ago saw many of its 5.1 million customers receive multiple bills and others receive none at all.

npower has reported profit from its domestic customers in the first six months of 2015 of £38 million, down 65 per cent from £95 million in the same period last year.

Chief executive Paul Massara said the first half of 2015 had been “very tough” for the company, but added other elements of the business were doing well.

Mr Massara said: "The main part of our drop in profits has been due to the continued impact of the systems issues that hit our domestic business last year.

"The challenges that we have faced were tougher than we expected but we know what the problems are and are taking the right steps to fix them."

He added he had personally written to all customers apologising for the problems with its billing system and pledged no one would be left out of pocket as a result.

But last month industry watchdog Ofgem ordered the company was ordered to give free power to customers who had been forced to wait more than 28 days for resolutions to complaints referred to the energy ombudsman.

However, the firm has also reported the operating loss in its generating division improved to £14 million from £74 million a year ago as a result of improvements in efficiency and increased demand for traditional power as opposed to renewable energy.

Mr Massara has voiced opposition to proposals by the Competition and Markets Authority that tariffs should be capped after it was found households in Britain were overpaying for their energy by about £1.2 billion as a result of failing to switch to better deals.

If the plans go ahead about 70 per cent of customers could see their bills frozen.

But Mr Massara said this would be “a retrograde step for one of the most liberalised markets in Europe”.

"We do not support the idea of a transitional safeguard tariff as we believe that it will harm customer engagement and reduce competition,” he said.

In the meantime the authority is also looking at scrapping variable rate deals, which are generally more expensive, and replacing them with capped tariffs.