The Competition Commission has revealed that 64% of CFOs and audit committee chairmen used to work for one of the Big Four firms.

Its findings were published in working papers looking into the alleged stranglehold of the Big Four in the UK audit market. According to the commission's survey, 64% of all respondents had previously drawn a salary from a Big Four firm.

The body also discovered that the majority of FTSE 350 companies would only consider engaging one of the Big Four firms for their audit, with 84% of FTSE 100 companies already actively embracing such an approach.

The dominance of E&Y, PwC, KPMG and Deloitte is underscored by the glacial pace businesses take to change their auditors. Over half of the FTSE 350 have remained with the same auditor for over 10 years, while 15% have never sought to change firms at all.

The watchdog is widely tipped to reveal the initial results of its probe into the apparently closed nature of the market amid claims from smaller auditors that fees are inflated, quality compromised and independence stifled.

And because so many ex-Big Four staff now chair audit committees and hold CFO posts, suspicions have been aroused that it may be underscoring the problem when choosing which audit firm to appoint.

The commission is also exploring the possibility that the wider market suffers because auditor interests are not in sync with shareholders who are effectively marginalised.

Both the European Commission and US audit regulators will be keen to digest the commission's findings, which were originally due for release in November, but have now been deferred until next year.