Speaking at yesterday's Reuters Global Media Summit, Sorrell said growth is "coming through stronger", with October's performance up 8% on last year.
Sorrell said: "We're seeing pretty good strength across the board," and added WPP had grown 4.5% from the start of 2010 to the end of October.
WPP owns advertising agency networks Y&R, JWT and Ogilvy & Mather, as well as media agencies MediaCom, Mindshare, MEC and Maxus.
Sorrell's comments come a week after GroupM, WPP's pooled media buying operation, again raised its forecast for growth in UK adspend to 7.7% in 2010 and 3.6% in 2011.
Yesterday it emerged WPP is backing a new international PR consultancy chaired by former Labour minister Peter Mandelson, Global Counsel.