WPP reported eight percent growth in 2014 four-month revenues to $5.7B, a performance slowed by a "marginally softer April."

The firm's PR/PA unit , which includes Finsbury, Cohn & Wolfe, Ogilvy, Hill+Knowlton Strategies, showed a 1.8 percent in like-for-like revenues, up from the 1.2 percent hike in the 2014 period. The segment grew everywhere but Europe.

CEO Martin Sorrell called WPP's financials "particularly credible" in an environment in which global GDP growth cooled during the second-half of 2014 and into this year.

He sees little chance of an "upside breakout" in global GDP, believing growth will be stuck in the three percent range.

Sorrell said though clients are more confident now than they were in the 2008 post-Lehman period, many remain risk-adverse.

He mentioned pressures to control costs brought on by various factors including the rise of activist investors Dan Loeb, Bill Ackman and Nelson Pelz.

The chief warned of the "lurking danger" that results from continual corporate cost-cutting.

"What were first adopted as temporary tactics almost imperceptibly become a permanent strategy," he wrote in the June 9 trading update.

"And when that happens, companies may fail to take early advantage of any upturn. The long-term becomes no more than an indefinite extension of the short-term."