All but one of 36 former colleagues called on by the NatWest Three to speak in their defence against Enron-related fraud charges have refused to meet the accused’s lawyers.

Documents seen by The Times show that lawyers for David Bermingham, Giles Darby and Gary Mulgrew wrote to 36 current and former employees of the Royal Bank of Scotland, which now owns NatWest.

The list of bankers, all of whom are being advised by RBS lawyers Travers Smith in London, includes Johnny Cameron, the bank’s chief executive of corporate markets.

Mr Cameron refused to comment about his reluctance to meet his former colleagues’ lawyers, adding that he preferred the moniker “the Enron Three” rather than “the NatWest three” as the men have become known.

Despite their plea, just one of the potential witnesses was willing to be contacted about giving evidence at the trial, which is scheduled to begin in October and could end with each of the NatWest Three serving 35 years in jail.

Sources close to their defence said that the lone former colleague who was willing to meet defence lawyers — whose identity has not been revealed — is reluctant to travel to the United States. That could potentially weaken the usefulness of his testimony.

A spokesperson for the NatWest Three said that they were determined to clear their names despite the setback: “They are particularly angry about having to face trial in the US rather than in the UK, and since much of what they argued in court in the UK about how their ability to defence would be compromised in Texas has proven to be true.”

Mark Spragg, the bankers’ legal representative in the UK, said that he thought it was “highly suspicious” that so few of the potential witnesses were willing to talk and that all — even those who have left RBS — were being represented by the bank’s legal advisers, Travers Smith.

Mr Spragg said: “The three have been trying to speak to 36 current and former RBS employees. It is highly suspicious that RBS’s lawyers now apparently represent all 36 witnesses and that 35 of the 36 have similarly refused to co-operate.”

An RBS spokesman said the matter was up to the individuals to decide. “In a case such as this, it is a matter for any individual whether they wish to accept such a request, and in view of the ongoing proceedings, it would be inappropriate to comment further,” he said.

Stephen Paget-Brown, a partner at Travers Smith, would not comment on his clients motivations, but denied there was a conflict of interest in his firm representing both RBS and the potential witnesses.

“It is absolutely clear that there is no question of there being a conflict of interest.

“There is no foundation or substance to the entirely misplaced inferences about our conduct and professionalism,” he said.

Under American law, the defence cannot approach the witnesses directly in this case, only through their lawyers. But criminal lawyers said that there were compelling reasons why potential witnesses may be reluctant to give evidence regardless of their feelings toward their former colleagues or whether they believed they were guilty or not.

Last month an inquest was told that Neil Coulbeck, another former colleague of the NatWest Three, killed himself over fears of being extradited to the US to face trial, also over the Enron scandal.

Mr Coulbeck, 53, from Woodford Green, northeast London, had received assurances from the FBI that he was in the clear. The coroner ruled that he had killed himself while the balance of his mind was disturbed.

It is unlikely that the NatWest Three would succeed in compelling the witnesses to testify against their will.

The bankers, who are under house arrest in Houston, are each charged with seven counts of fraud.

They are alleged to have conspired with Andrew Fastow, Enron’s former finance director, to execute a complex financial scam that cheated NatWest out of several million dollars.

Mr Fastow, jailed for six years for his role in the collapse of Enron, has agreed to testify against the three men in return for a lighter sentence.

If convicted of all charges, they each face a maximum of 35 years behind bars.

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