Scottish Power said it had absorbed wholesale prices as long as possible

The company is raising electricity prices by between 5% and 8% from 17 October and gas by 12%. But it is also offering customers capped prices.

In September Scottish Gas announced it was increasing its prices by 14.2%

Willie MacDiarmid, of Scottish Power, blamed wholesale prices and said the company had protected customers from increases as long as possible.

The energy retail director said: "Like all energy suppliers, Scottish Power has been hit by the unprecedented rise in wholesale prices.

That prices are going up at a time of year when energy consumption increases and forecasters are warning of a harsh winter is at best unfortunate Graham Kerr Energywatch Scotland

"We have frozen prices for as long as possible, but unfortunately are now forced to pass on part of this increase to customers."

A spokesman said Scottish Power's standard gas and electricity offer would still be cheaper than many of its main rivals including British Gas.

He said the increases were in response to the continued steep rise in wholesale energy costs, up nearly 70% since April 2004.

Customers are being encouraged to protect themselves from further increases for two years by switching to Scottish Power's Capped Price Offer which will shield customers from further increases until October 2007.

The company said customers who pay by cheque could save up to �64 a year by switching to direct debit.

'Blow for households'

It is also offering a package of measures, including insulation grants which can save an average household up to �200 a year.

Scottish Power has also restricted the increase for prepayment electricity customers to between 5% and 6%.

The Scottish National Party's energy spokesman Richard Lochhead, condemned the rises.

"This latest rise is a blow for households across Scotland," he said.

"With every 5% increase, 30,000 Scots are plunged into fuel poverty. It is ridiculous that this should happen in an energy rich nation.

"It is unacceptable that the people of Scotland are paying the consequence from not having control of energy policy to achieve self-sufficiency and security of supplies."

Energy consumption

Energy watchdog Energywatch said that despite having lower electricity price rises than its competitors, Scottish Power remains Scotland's most expensive electricity supplier.

Graham Kerr of Energywatch Scotland said: "That prices are going up at a time of year when energy consumption increases and forecasters are warning of a harsh winter is at best unfortunate.

"In a bid to reduce the impact of the price rises Energywatch Scotland urges all consumers to keep their bills in check by sensibly reducing their energy consumption, switching to cheaper payment methods such as direct debit and shopping around for a better energy deal."

He said the rises added �23 to the average annual electricity bill and �48 to gas bills.

Since 2003, Scottish Power's prices have risen by 31% for gas and 27%.