WPP acknowledged today that growth during March was slower than expected despite strong sales from a resilient US advertising market.

Shares in the company fell 5.4 per cent to 596p after it said that while January and February were strong across the group, March was "somewhat surprisingly" slower in continental Western Europe, particularly in Germany, France and Spain.

Sir Martin Sorrell, the group’s chief executive, said that March was a “strange month”.

Revenues for the first quarter rose by 14.1 per cent to £1.56 billion in the first quarter of 2008.

On a like-for-like basis, revenue growth was up almost 5 per cent.

Despite the wider economy experiencing a slowdown, WPP said that North America continued to "grow faster than commentators might expect", with like-for-like revenues up over 5 per cent, an improvement on the last half of 2007.

"North America, despite the talk of recession and the continuing credit crisis affecting the major financial institutions in the United States, remains strong," WPP said in a trading update this morning.

Britain, however, was the group's slowest-growing region.

WPP said that Eastern Europe was now its fastest-growing region, marginally ahead of the Middle East, with revenue growth of 21 per cent.

Latin America was also strong, with growth of 15 per cent, while in Asia Pacific revenues rose 6 per cent.

Mainland China and India continued the rapid growth seen in 2007, with first-quarter like-for-like revenues up 19 per cent in both markets.

However, Sir Martin said that he expected softer growth in China in 2009.

"No economy can grow at 10 per cent compound forever," he said.

Sir Martin has reiterated that he is expecting 2009 to be a slower year for the group than 2008.

The group said in the statement that it was in the process of compiling its first-quarter full-year forecasts, and early indications show that like-for-like revenues are growing faster than in 2007.

The group said that net new billings of £564 million were won during the first quarter.

WPP, which has seen its shares fall by roughly 20 per cent in the past year, has proved to be one of the stronger players in the media sector.

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