Npower has been rapped by industry watchdog Ofgem for not doing enough to help customers who struggle to pay their bills.

The energy giant, which has the highest customer disconnection rate of all the major power suppliers, announced price hikes of 17.2 per cent for gas and 12.7 per cent for electricity for its 4 million customers which took effect from January 5.

Ofgem said npower cut off 70 gas customers per 100,000 in 2006 for non-payment of bills compared to EDF Energy which had the second highest rate of around 37 customers per 100,000.

Other rival firms E ON, Scottish and Southern Energy and Scottish Power all disconnected between 20 and 25 gas customers per 100,000 in 2006.

At the end of 2003, British Gas stopped disconnecting customers but has warned Ofgem this could be resumed after 2008.

Ofgem said the total number of UK customers disconnected for non-payment of their energy bills rose from 2,913 in 2005 to 5,117 in 2006. Initial figures for 2007 suggest the rate for that year will be around 5,000 disconnections.

Npower fared the worst out of all the UK's major energy suppliers in dealing with customers in debt and Ofgem said procedures must be improved to bring them into line with industry best practice.

Ofgem chief executive Alistair Buchanan said: "At a time when some energy suppliers have announced double-digit price rises, it is vital that suppliers ensure they are offering the best support to people in debt or danger of falling into debt.

"This is why npower must do more to match the best practice set by leaders in this field."

In a statement, npower said it would continue to review its debt management processes.

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