KPMG has overtaken PWC as the UK's leading auditor in terms of overall client numbers, according to the latest research from Adviser Rankings. In its second quarter 2012 Corporate Advisers Rankings Guide, KPMG moved up into top position for the most number of UK quoted clients, though PwC's client base remains more profitable and is larger by aggregate market cap. The merger between BDO and PKF has seen the combined entity leapfrog Grant Thornton as the largest auditor of AIM clients and replace it as the fifth-largest auditor of all listed companies. The newly merged entity's net gain of 27 AIM clients was accompanied by a 19% increase in market-cap to £6.47bn. CCW and UHY both gained clients and moved up a place in the overall rankings to eighth and ninth respectively. However, client numbers for both Deloitte and Ernst & Young reversed over the period. In terms of auditing the largest companies, PwC remained the largest auditor of FTSE 100 businesses with 43 clients, more than double the number held by Deloitte, which moved into joint second place with KPMG.