According to the US Centre for Public Integrity, Mr Lay and Enron donated more than $500,000 to Bush campaign coffers – making Enron the president’s largest single patron.

The president is a friend of Mr Lay, who he apparently refers to as “Kenny Boy".

Mr Bush has championed some issues Enron considered important, such as deregulating utilities and limiting compensation awards. He has also favoured more oil exploration and drilling in spite of opposition from environmentalists.

As a former Texas oil executive, Mr Bush is seen as friendly to the oil and energy industries.