The UK is the worst performing region for WPP so far this year. However, Sorrell said conditions remain positive for the media planning and buying sector as a whole.
Last week WPP announced its first half revenues for the six months ending June 30, with the UK growing by only 1.2%, compared to 9.4% for Asia Pacific, Latin America, Africa and Middle East, 4.5% in North America and 4.5% in continental Europe.
But media fragmentation in the UK particularly had also resulted in stronger operating conditions for media planning and buying companies, said Sorrell, as media spending decisions had become "more complex" for clients. He said they need more advice on "how to spend and where to spend".
Group M, WPP's UK media buying powerhouse, including MediaCom, MindShare and Mediaedge:cia, has grown 12% year on year.
The impact of internet advertising has been greater in UK compared with other markets, added Sorrell. He cited a recent Group M report which has forecast that by November, internet advertising in the UK will account for 14% of all adspend.
"That is stronger than the global average which is 7% and Spain which is only 2%. It has overtaken radio advertising and is now the same as national press advertising," said Sorrell. "Our industry is becoming more and more two-paced. Slow growth in traditional media such as network television, newspapers and magazines, more rapid growth in new media, such as direct, internet and interactive."
Globally, WPP Group reported pre-tax profits were up almost 30% for the first half of the year to £287m on revenues of £2.86bn. The group won estimated net new business billings of £2.2bn.