In the latest analysis of the audit market, conducted by Accountancy, the FTSE 100 audit market was valued at £534m, with audit related fees and non-audit fees pushing the total beyond £784m. The market is dominated by the Big Four firms, with only BDO handling one FTSE 100 audit for Randgold.

The changes, which will take effect on 21 March, also see Deloitte losing one FTSE 100 client, as Hikma Pharmaceuticals falls out of the list, but picking up a replacement in publishing company Informa, which enters the FTSE 100 for the first time.

Investment company Aberdeen Asset Management is also dropping out of the stock exchange, which is a loss for auditors KPMG. However, the firm is also the auditor to newly merged gambling company Paddy Power Betfair which now enters the FTSE 100.

Engineering company Smiths Group, which is audited by PwC, is the fourth company to leave the FTSE 100.  PwC is the auditor to the two other companies which are now included in the top tier. The first is supermarket chain WM Morrison, which is rejoining the FTSE 100 after a demotion last year in the autumn quarterly review. 

The second is South African-based private hospital operator Mediclinic International, which has undergone an expansion via a reverse takeover. The Mediclinic audit is a recent win for PwC, with the healthcare company announcing in February that PwC will be taking over from KPMG for the 2015/2016 financial year.

The FTSE 100 is reviewed four times a year by the Stock Exchange, with companies promoted if their market capitalisation is ranked 90th or above on the decision day, and demoted if ranked 111th or below.  

To find out more about the FTSE 350 auditors, read our annual in-depth analysis and league tables at FTSE 100 Auditors Survey and FTSE 250 Auditors Survey