The high-profile case of the three former NatWest bankers, accused of fraud, is expected to boost directors' and officers' (D&O) policy sales.

Insurers are understood to have been inundated with D&O policy queries from company executives, concerned by the recent extradition of the so-called NatWest Three, David Bermingham, Giles Darby and Gary Mulgrew. But experts said that premiums are not expected to rise.

Gary Head, director of Hiscox' professions and specialty commercial division, said: "It is a growing market and there are a lot of companies and directors who are still not fully aware of their obligations and liabilities.

"[The NatWest Three case] is just another perfect example of the threat to directors of companies where a D&O policy would certainly protect those individuals against proceedings."

Head said that with the increase in D&O claims and the global economy becoming more electronic with intercontinental trading, there was now an increased obligation and responsibility on directors of large corporations and small to mid-sized businesses to purchase suitable insurance.

According to Datamonitor, the D&O market currently produces £500m in premiums, which could rise to £800m by 2008.

Adam Codrington, executive director in Aon's professional risks unit, said the NatWest case was unlikely to result in raised premiums.

He said: "It would be an overreaction if insurers looked to raise the price of D&O cover or charged extra to cover the threat of extradition, but buyers will need to pay for increased focus on their policy wordings."