‘USA, USA,” shouted Ian Russell, the chief executive of ScottishPower. He was at Cardiff’s Millennium Stadium on May 21 with his son, watching the FA Cup final.

As the game went into extra time, the Arsenal fans began mocking their opponents, Manchester United, and their new American owner, Malcolm Glazer. Russell could not help himself. He had to join in.

But as Russell bellowed about the trouble America was causing one business he knew that America was also causing problems for his own company. The chance to shout about one American acquisition offered welcome relief from the prospect of another Russell had been agonising over, and about which he had kept silent.

Three days later, he stunned the City by announcing the sale of ScottishPower’s troubled American unit, PacifiCorp, after six years of profit warnings and management upheaval. The buyer was another American billionaire, the legendary investor Warren Buffett, who acquired PacifiCorp through MidAmerican Energy Holdings, a company owned by Buffet’s investment trust, Berkshire Hathaway.

The scale of the deal put the £790m purchase of Manchester United in the shade. Buffett paid $9.4 billion (£5.2 billion) for PacifiCorp.

Shares in ScottishPower rose 6.3% to 469Çp on the news, and ended the week on 466Äp, but the company and Russell himself may now face a battle to save themselves. While some among ScottishPower’s shareholders have welcomed the deal, others may see Russell’s U-turn as one mistake too many. For years, he had talked of the importance of PacifiCorp. Now he had decided to sell it at a loss of almost £1 billion.

ScottishPower may now struggle to maintain its independence. A merger with its bitter rival Scottish and Southern Energy seems the most probable result, but Centrica and the German utility giant Eon are also expected to be knocking on Russell’s door.

The final decision to sell PacifiCorp was made during an exhausting round of all-night talks led, on one side of the Atlantic, by Russell in ScottishPower’s London office and on the other by David Sokal, the chairman and chief executive of MidAmerican.

The next morning Russell used ScottishPower’s annual results announcement to break the news.

A day later he was worn out but determined to defend his decision. “The market perception was that I had too much personal capital tied up with PacifiCorp, that I would never sell it, that I would never do the right thing for shareholders,” he said. “When we came out on Tuesday and did the right thing, I think the market was surprised.”

PacifiCorp has long been seen as Russell’s baby. He was the deputy chief executive of ScottishPower when the decision to buy the company was made and has since spent one week every month in America trying to sort out the business.

In November, he admitted PacifiCorp had continued to disappoint and that operating profits would be flat for the next two years.

Unknown to those outside the company, Russell had commissioned a review of PacifiCorp; in October 2003 a Citigroup note suggested he break up ScottishPower, with PacifiCorp the obvious target.