Energy firm Npower is to cut up to 2,500 jobs, more than a fifth of its UK workforce, with an announcement to staff expected this week. Npower, which is owned by the German energy giant RWE, employs 11,500 people in the UK and is one of the country's big six gas and electricity suppliers. The BBC understands sales and marketing roles will be the worst hit. The company, which has not made any official comment, posted a loss of £48m for the first nine months of last year. It has also lost about 200,000 UK customers. RWE will announce Npower's full-year results on Tuesday when it is expected to detail the planned job losses. The German company, which also generates and distributes energy, has been hit by oil prices falling more than a third in the last year to around $38 a barrel.