It contains no surprises, but rather confirms what we knew – the four largest firms are auditors of choice to the FTSE 350, largely because they are seen to have greater capacity and international coverage, the best people, industry specific knowledge, and to provide relevant ‘value added services’.

Oxera also found that companies place a high value on being associated with the reputation of a Big Four auditor.

So, is there a problem? Most respondents said they would welcome greater choice.

However, less than 10% of FTSE 350 companies would consider using a mid-tier firm, and it is hard to argue that the reasons they have given for selecting a Big Four firm – reputation, sector specific skills, international coverage and quality of staff – are not in the best interests of their shareholders and the wider capital markets. It should not be overlooked that this is a market of powerful buyers.

In my view, four is enough, five may be better, but not at the cost of any reduction in audit quality.

So, should anything be done? Oxera rightly identifies that new rules on auditor independence have restricted choice, and I would advocate a review to see where some sensible relaxations could help without impairing auditor objectivity.

The long-awaited liability reform should make the top end of the market more attractive to smaller firms, particularly if the reform spreads internationally.

The idea of publishing AIU reports into individual audit firms is worthy of further discussion, with buyers of audit services to establish what kind of information is needed to inform their purchasing decisions and how best this information might be conveyed to the market.

Beyond these possible measures, however, a market, not regulatory, solution is required. Oxera identifies ‘significant barriers to entry’ to the FTSE 350 audit market, namely the need to acquire a ‘credible reputation’, an ‘extensive and integrated international network’ and ‘substantial resources and expertise’.

Achievement needs ‘significant investment’ and a ‘long investment horizon’ in the way the partners in my firm have made a sustained investment over the past 30 years to be able to provide exactly what our clients say they need.

Liability reform might just provide the trigger to encourage a new entrant. The question now is whether anyone outside the Big Four has the appetite to make the necessary long term investment.

Peter Wyman is head of professional affairs at PricewaterhouseCoopers