The company took over from Klynveld Peat Marwick Goerdeler (KPMG) who have held the position for six years.
The latest report from Adviser Rankings made the revelation.
In the report, the recent merger of BDO and Moore Stephens pushed to third place, overtaking Deloitte while Ernst & Young (EY) remained in the fifth position.
PKF Littlejohn has moved up to eighth place in overall clients following its Welbeck Associates tie-up.
PwC has regained its lead among the FTSE 100.
For the first time since 2005, it was knocked off top spot KPMG.
PwC has now recaptured its position, adding Hikma Pharmaceuticals and Hiscox.
However, it lost the lucrative contract of Vodafone. The telecommunication company PwC replaced with EY after a firm that PwC was administering considered legal action.
KPMG revealed in November that it had has decided to stop performing non-audit work for FTSE 350 clients.
The decision was aimed at restoring public trust in the audit sector following a number of recent scandals, including the collapse of Carillion and British Home Stores (BHS).