Big four audit firms 'do not collude over market share In a working paper as part of a wider investigation of competitive problems in the audit market, the Competition Commission said that, although the market dynamics appeared to be conducive to "tacit" collusion, by which firms implicitly agree not to compete rather than make explicit arrangements, it could find no evidence for this. The paper will be welcomed by the big four accounting firms - KPMG, Ernst & Young, PricewaterhouseCoopers and Deloitte - but a fuller report on the commission's findings due in November may yet decide there are irregularities. According to the commission, between 2002 and 2010, the big four audited more than 90pc of the FTSE 350 companies and accounted for 95pc of FTSE 350 audit fees, and their dominance has increased over the period. Mid-tier firms BDO and Grant Thornton told the commission the market was conducive to "tacit" collusion and urged it to look at the big four's pricing behaviour. However, despite "high concentration, significant barriers to entry, [and] switching costs," the commission said: "We do not currently have the further evidence necessary to establish that there has been tacit co-ordination." It added that "this position would change" if its ongoing investigation came up with new evidence.