The Big Four now audit all of the UK’s FTSE 100 companies for the first time since November 2008, according to Adviser Rankings, despite numerous reports which have called for their dominance to be curbed.

Earlier this year, the UK’s Competition and Markets Authority (CMA) launched a report offering a number of proposals to help increase competition in the FTSE 350 market, including the introduction of joint audits so that mid-tier firms would have easier access to that market.

While many firms and institutes have voiced their support for reform in the market, the notion of joint audit faced criticism due to the perceived lack of evidence that it would improve audit quality and fears that it may solidify a view of the Big Four as being superior if they are the lead auditors in a Big Four/ non-Big Four joint audit.

Although these proposals are still being considered, and it could take a significant amount of time before they come into legislation, the lack of non-Big Four firms providing audit services for the FTSE 100 only further highlights the lack of competition in the market.

Outside of the upper end of the market, BDO still retains a significant lead in the AIM rankings despite losing three clients. Grant Thornton took second place over KPMG with the addition of four clients, taking its total up to 116 clients.

In the FTSE 250 the running order remained the same in terms of client numbers, though KPMG took first place by aggregate market cap.