Nine out of 115 senior people interviewed by the Financial Services Authority in the past nine months to take top roles at banks and other “high-impact” financial services firms withdrew their applications after failing to come up to scratch.

Today the City regulator said it was making its rules even tougher for people who held roles of “significant influence” at such firms.

The move is aimed at tightening up the management and boards of directors at between 40 and 50 firms which the watchdog believes are the most important in the markets. In particular the FSA warned non-executive directors they could face action from it if they fail to intervene quickly and actively in management decisions.

This follows sharp criticism of such directors at banks like Northern Rock, Bradford & Bingley and Royal Bank of Scotland, who were said to have failed to question the actions of strong executive directors.

The new rules are also being extended to cover all traders who deal on a firm's own account, an area where several rogue traders have been unearthed in the past couple of years.