Sir Martin Sorrell, chief executive of WPP, has today pointed to factors such as the "pressure" that ITV is under for the continued lagging performance of his company's UK advertising business.
Globally, WPP, the world's second-largest marketing services group, performed well, reporting a 30% increase in first half pre-tax profits to £287m.
WPP won estimated net new business billings of £2.2bn in the first half of the year.
However, among WPP's regional businesses around the world the UK was a poor performer, registering revenue growth of just 1.2%.
This compared with growth of 9.4% for Asia-Pacific, Latin America and the Middle East, 4.5% in north America and 4.5% in continental Europe.
The company said trading in western Europe was "relatively more difficult", although it has "improved over last year", with the UK "stabilising, at low levels of growth".
It described WPP's overall performance as "record first-half results, reflecting continued significant improvement over last year and further evidence of growth across the whole business".
Like-for-like revenues were up 5% in the first half of 2006, a slight increase on growth of 4.8% in the first quarter of the year.
The company, owner of agencies including JWT, O&M and MindShare, said revenue rose 16% to £2.86bn in the first half of 2006.
Operating profit is up more than 20% to £361m, from £299.6m in the same period last year.
Operating margins rose to 12.6% from 12.1%, in line with the full year margin target of 14.5%.
Mr Sorrell said: "I think the UK will stay around these levels for the rest of the year - it isn't that vibrant or strong.
"This is understandable as there are major structural changes occurring in the market. Look at network TV, such as ITV - it is under pressure. And who would have thought that Daily Mail & General Trust would consider selling off Northcliffe Newspapers?," he added.
"The impact of the internet in the UK has perhaps been more sharp [than in other markets]."
As evidence he pointed to a recent report by WPP media planning and buying arm GroupM, which has forecast that by November internet advertising in the UK is set to account for 14% of all ad spend - overtaking the share held by national newspapers.
This compares, said Mr Sorrell, with a global average in mid-single digits and some markets, such as Spain, at just 2% of all ad spend.
The global shift in the structure of the advertising market was evident in acquisitions such as Rupert Murdoch's News Corporation buying MySpace and ITV buying Friends Reunited, Mr Sorrell said.
While traditional creative ad agencies - but not media planning and buying agencies - were "under the gun", those operating in the digital and mobile arena were doing well, he added.
As a group, direct marketing and digitally-related activities now account for 20% of WPP's revenues, which are about $11bn (£5.8bn) a year.
Putting his "finger in the wind", Mr Sorrell said he expected those areas to grow to one-third of all revenue in the next five to 10 years.
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