Only one former executive has been jailed so far

Wesley Colwell, head of accounting at Enron North America, has agreed to pay $500,000 as part of a settlement, in which he neither admits nor denies wrongdoing.

The SEC accused Mr Colwell and others of taking part in "a wide ranging scheme to defraud by manipulating Enron's publicly reported earnings through a variety of devices designed to produce materially false and misleading financial results."

This involved, the SEC said, misusing reserve accounts, concealing losses, inflating asset values and improperly accounting for transactions.

In particular, the SEC alleges that Mr Colwell was behind the concealment of over $1bn in losses at the firm's retail business, retail energy business, Enron Energy Services.

Mr Colwell is the latest in a string of former officers at Enron and associated companies to be hit with civil charges since the firm's collapse at the end of 2001.