Average bills for dual fuel customers are set to rise by �131

Energywatch Scotland described the increase as "a brutal assault" on consumers from a company which has just posted record profits.

The utility firm said gas bills were set to increase by an average of 17%, while the cost of electricity would rise by 10%.

The Glasgow-based company blamed rising wholesale costs for the hike.

Last month, it warned that price rises were likely, at the same time as it unveiled a pre-tax profit jump of �675m, 47%, in the past year.

Scottish Power had already increased its gas prices by 15% and electricity by 8% in March.

We now need to pass on some of these increased wholesale energy costs Willie MacDiarmid Scottish Power Have Your Say: Scottish Power price rises

The company's director of energy retail, Willie MacDiarmid, said: "As we indicated last month, wholesale energy costs continue to rise and are now a record 80% higher than this time last year.

"We have absorbed most of the impact and our last price increase announced in February was one of the smallest in the sector.

"However, we now need to pass on some of these increased wholesale energy costs."

'Hard to understand'

Energywatch Scotland spokesman Graeme Kerr said: "Scottish Power customers will find it hard to understand why a company that has just posted record profits needs to raise prices on such a huge scale.

"Customers who take both gas and electricity from Scottish Power will be paying, on average, �131 more per year as of next month.

"Scottish Power will be the second most expensive energy supplier in Scotland. Only Scottish Gas will remain less competitively priced."

Rising prices are said to be creating debt problems

David McNeish from Citizens Advice Scotland said that the prices rises were a "significant" issue in rising debt problems.

"The sad thing is we have made some progress on reducing fuel poverty but it has been wiped out by price rises," he said.

Mr McNeish said vulnerable groups, such as those on long-term sickness and disability benefits, were particularly badly affected.

He said that pensioners were offered support in the form of winter fuel payments, central heating upgrades and household insulation, but these were not available to other vulnerable people.

Scottish National Party energy spokesman Richard Lochhead said: "It seems that it is the customers who are taking all the pain and not the shareholders of Scottish Power."

He called for an energy summit of all major suppliers to address the growing problem of fuel poverty.