In a high-risk manoeuvre, defence lawyers in the Enron trial will next week call the company's former CEO Jeff Skilling into the witness box.

Former CEO and chairman Ken Lay is also expected to take the stand but Mr Skilling's testimony could prove more challenging for the defence, not least because he has said so much about the energy giant's collapse already.

On his way into court yesterday, Mr Lay predicted that Mr Skilling would make "a great witness", helping to dispel suspicions that they could turn on one another in the witness box.

When Mr Skilling faces cross-examination, he will be confronted with contradictions between his evidence and that of other former Enron executives. He may also be haunted by his statements to a congressional inquiry into the firm's collapse and to a Securities and Exchange Commission (SEC) investigation.

Mr Skilling faces 31 counts of fraud, conspiracy, insider trading and lying to auditors about Enron's financial position and Mr Lay faces seven counts of fraud and conspiracy. Prosecutors say the two men gave false assurances to the investing public that there were no problems at Enron when they knew that the energy giant was built on sand.

Once the US's seventh largest company, Enron collapsed after it emerged that an estimated $40 billion (€32.6 billion) of debts had been hidden in secret accounts to protect the firm's balance sheet.

Enron had more than $68 billion in market value before its bankruptcy wiped out more than 5,000 jobs and at least $1 billion in retirement funds.

Mr Skilling is a former McKinsey consultant who exudes intellectual confidence and relishes a bare-knuckle argument.

Unlike most other Enron executives, who pleaded the Fifth Amendment to avoid testifying to congress, Mr Skilling appeared eager to justify himself. He told congress he was innocent of criminal conspiracy and that Enron's collapse was caused by nervous investors who started a stampede away from the company.

"It is my belief that Enron's failure was due to a classic run on the bank, a liquidity crisis spurred by a lack of confidence in the company. At the time I left the company, I fervently believed that Enron would continue to be successful in the future," he said.

In his secret testimony to the SEC in December 2001, which was published for the first time this week by the New York Times, he went into greater detail, insisting that Enron took every precaution to ensure that everything was legal and nothing was hidden or improper. Mr Skilling said that if anything illegal had occurred, he could not be expected to know about every transaction because the company was too big for any one person to control. "Obviously, I couldn't see the whole company. I mean, this was a gigantic company." Prosecution witnesses have already contradicted a number of Mr Skilling's key claims in testimony to the SEC.

He told the SEC that Enron never used reserves to help the company meet Wall Street earnings expectations and that there was never a last-minute rush to meet earnings expectations towards the end of a quarter.

Several witnesses, including former Enron accountant Wesley Colwell, have testified that Enron used accounting reserves to lift the company's earnings in particular quarters and that last-minute efforts were often made to meet Wall Street projections, requiring manipulations involving a penny or two of earnings per share.

Mr Skilling told the SEC he had not been aware of any problems with Enron's use of special-purpose entities that resulted in the company's shifting debt off the books, although a number of former executives have pleaded guilty to criminal charges in connection with these entities.

"I had absolutely no reason, given the process and the sign-offs, to have any expectation that the accounting did not properly reflect . . . the way the transactions were structured," he said.

Despite his reputation as a hands-on manager, Mr Skilling claimed that he was at best a casual reader of Enron's financial statements, placing his confidence in the company's accounting controls. "I can't tell you I read them, you know, cover to cover. I felt by the time that process was completed that it was a fair and accurate presentation of what was going on in the company," he said.

Mr Skilling's indictment has taken a heavy toll on his health and a judge eventually ordered him to attend alcohol treatment and community-service programmes after passers-by called authorities to report him behaving erratically on Manhattan's Upper East Side.

Unlike Mr Lay's family, Mr Skilling's wife and children have mostly stayed away from the courtroom in Houston where a jury will decide if the former executive will spend most of the rest of his life behind bars.

Some legal experts have expressed doubts about the wisdom of allowing Mr Lay and Mr Skilling to testify, pointing out that WorldCom's Bernie Ebbers and Tyco's Dennis Kozlowski were convicted of fraud after they took the stand.

As he left the courtroom yesterday, Mr Skilling appeared to be looking forward to giving the performance of a lifetime next week. "I've got nothing to hide. I am innocent of all the charges."