The Office of Fair Trading (OFT) has referred the audit market to the Competition Commission (CC) for further investigation.
Following a public consultation, it referred the market for the 'supply of statutory audit services to large companies' to the commission. At present the Big Four earn 99% of audit fees paid by FTSE 100 companies.
According to an OFT statement, it has been concerned for some time that the audit market is highly concentrated, with low levels of switching and substantial barriers to entry.
Between 2002 and 2010 the average annual switching rate among FTSE 100 companies was just 2.3%.
The OFT has also considered the potential for overlap with parallel work ongoing at a European level. However, the nature, content and timing of EU legislation are not settled and the OFT believes that there are a number of important inputs that the CC might make during the legislative process.