Scottish Power was the larger of the two Scottish energy companies and benefited from being both a generator and supplier of power. In 1995 it acquired the English Regional Electricity Company Manweb, which supplied Merseyside and North Wales. In 1996 the company diversified into the water supply business with the purchase of Southern Water (which was sold again in 2002). When the supply of energy into British homes was opened up to competition, ScottishPower entered this market, stealing share from the previous gas supply monopoly British Gas and also building new market share in England and Wales.
Scottish Power established the telecommunications company, Thus (originally known as ScottishTelecom). This was floated on the London Stock Exchange with Scottish Power retaining a 20% stake, until 2002 when it sold its interest.
In 2000, Scottish Power completed the acquisition of Pacificorp which supplies electricity in the western United States, where it operates as Pacific Power (in Oregon, Wyoming, Washington, and California), and as Utah Power in Idaho and Utah). In May 2005 Scottish Power announced that it had agreed to sell Pacificorp to MidAmerican Energy Holdings Company for $5.1 billion in cash and $4.3 billion in debt and preferred stock. The successful completion of the deal was announced on 21 March 2006, after securing regulatory approvals. The deal did not include PPM Energy, as Pacificorp Power Marketing was formerly the non-regulated subsidiary of Pacificorp. Scottish Power intends to return a large proportion of the proceeds to its shareholders.
Rejected takeover bid from E.ON
Following the announcement, the group's share price rose, but were now widely seen as vulnerable to a takeover. It was soon revealed that German energy group E.ON, who also own Powergen, were interested in a takeover. On November 22 2005 the board rejected an offer from E.ON of 570 pence a share, which would have valued the group at £10.7 billion. 
Takeover from Iberdrola
On November 28, 2006, the board of directors of Scottish Power agreed to a £11.6 billion takeover bid by the Spanish energy firm Iberdrola (Spain's second-largest utility company) to create Europe's third-biggest utility and a world leader in renewable energy.  The new group will have installed capacity of 36,600 megawatts (MW), of which over 6,000 MW will be renewable, and its electrical supply points will total 21.4 million. Iberdrola, the hundred-year-old Spanish-based company, is among Europe’s major electrical companies and operates gas and electricity businesses in 28 countries. In addition, it is one of the world leaders in the production of windgenerated power.
The Board of Directors of ScottishPower had been advised on this merge by Morgan Stanley who controls approximately 0.1% of the company's capital. 
- ^ Photograph from ScottishPower Energy Networkshomepage, accessed 1 April 2007.
- ^ Photograph from AEM Iberdrola, logo, accessed 16 April 2007.
- ^ Takeover information from CNN.com World Business,"Scot Power agrees $22B Spanish bid", accessed 16 April 2007.
- ^ Takeover information from Iberdrola Press Release, "IBERDROLA REACHES MERGER AGREEMENT WITH SCOTTISHPOWER FOR € 17.2 BILLION", accessed 16 April 2007.