Even when you already know something, it can still be helpful to hear it again. That is the case with yesterday's report on the dominance of the Big Four audit firms. It is scarcely a surprise that the four - Deloitte, Ernst & Young, KPMG and PwC - dominate the audit market for large listed companies in the Group of Seven leading economies and many other countries, and that this concentration produces disadvantages in the market from such limited choices. Even so, the in-depth study of the Big Four's grip on the UK highlights some points that must be addressed if this unhelpful and possibly unhealthy position is to change.

The government-commissioned report by Oxera, an economic consultancy, found that firms just below the Big Four faced barriers to entry in auditing large listed companies that were matters both of fact and of perception. For example, the investment case for expanding in the hope of being appointed by the largest companies was unattractive when their realistic prospects of success were very small. The survey of audit committees found that many believed investors would be concerned about appointing outside the Big Four and that they knew much less about the mid-tier firms in general.