ScottishPower supplies four million customers

It made a profit before tax of �920m last year, slightly more than the City had been expecting.

The firm now has more than four million customers in the UK, while its American operation PacifiCorp also improved its performance.

Chief executive Ian Russell said the company was well-placed to fully exploit opportunities for growth on both sides of the Atlantic.

Mr Russell said: "Increasing demand and the need for more reliable and sustainable energy present attractive opportunities for organic growth and higher returns.

"We expect to invest �1.2bn in the current year of which around half will be for organic growth.

Price rises

"We remain confident that our strategy will create further value for shareholders."

Energywatch Scotland, the gas and electricity watchdog, criticised the rise in UK profits, which increased from �78m to �101m.

Chairman John Hanlon said the success highlighted concerns over high electricity prices in Scotland.

Mr Hanlon said: "ScottishPower blamed this year's 6% price rise on rising costs yet they have managed to increase profits by 30%.

"It is particularly galling that those price rises hit local loyal customers before being phased in elsewhere."