The role of the auditors, KMPG, in failing to uncover mis-pricing of options stretching back to 1994 is also being investigated in stage two of NatWest's review.
Last week, NatWest Markets suspended four more senior staff while the investigation, by internal audit and teams from accountants Coopers & Lybrand and top City lawyers Linklaters & Paines, proceeds. It increased the estimate of losses from pounds 50m after a worldwide review of its derivatives book and slashed bonuses by pounds 8m.
The Serious Fraud Office has been contacted, although Nat- West stresses that no client has suffered losses and no evidence of conspiracy has been found.
The latest suspensions follow that two weeks ago of Neil Dodgson, the supervisor of Kyriacous Papouis, the dealer thought to be responsible for concealing the losses.
"I would be surprised if we didn't make more announcements in the future. The auditors must be as much in the firing line as everybody else," one senior NatWest executive said.
This weekend, it emerged that Mr Papouis' girlfriend, who still works for NatWest Markets, has also been sent on paid leave.
Sources say, however, that she works in a different area and is not thought to have played any role in the affair.
Mr Papouis resigned at the end of last year and has since left his new employer, US investment bank Bear Stearns.
Senior bank sources say the review is likely to lead to a thorough shake- up of NatWest Markets' management of trading, though the board is standing by its chief executive Martin Owen.
This weekend, to stave off further calls for Mr Owen's head, the bank reiterated that it had only put an initial figure on the losses hours after it announced it results on Tuesday, 25 February.
By the Friday, after market rumours and press inquiries, it still had not quantified the losses fully but put out the announcement to stop damaging speculation, a spokesman said.
Mr Owen, a former Salvation Army officer, last week agreed to forgo pounds 200,000 of his pounds 500,000 bonus for last year.
NatWest insiders were surprised over the suspension of Phil Wise, NatWest Markets' chief administrative officer, in the latest round. The bank insists the move is just to "put people into neutral" while the review goes on. Mr Wise, however, is one of its high flyers, is very close to Mr Owen and has been tipped as a potential chief executive of the clearing bank itself.
"If ever there was a time for the maxim 'greater love hath no man than to lay down his life for a friend', this is it," one NatWest insider said.