The announcement effected its UK shares, dipping to a three-year low of 178p on Thursday, recovering slightly. This morning shares in TNS were trading down 4% or 8p at 186.75p.
TNS said the the performance across the rest of its business had been strong, but its US business has not recovered as anticipated this year and a significant restructuring of that business has taken place. As part of the US review, a new president of TNS North America, Kimberly Till, was appointed in May.
Till has been tasked with increasing the firm's sector knowledge and focusing on customer service, and is part of a reorganisation that the firm hopes will achieve cost savings of £10m, which will partly be reinvested in the future growth of the business.
David Lowden, TNS chief executive, said: "The performance of our American custom business in the first half has been unacceptable and this has held back an otherwise good performance."
The firm, which counts Coca-Cola and Procter & Gamble among its clients, cited spending cuts in a large technology client and increased competition from the internet as a source of information as its main challenges.
"As the internet brings down the cost of data collection in the US, the volume of research being commissioned there is rising. In all regions, there is rising demand from newer users of market information, such as the technology sector," Lowden said.
TNS, which operates across 70 countries, said that underlying revenue growth for the group in the first six months is expected to be around 3%. In the UK it reported a return to growth during the second half of 2005, with the company delivering underlying revenue growth of 4.1%.
In Asia-Pacific, TNS continues to perform very strongly and is expected to show excellent growth for both the half and full year.
Looking forward TNS said that the pattern of revenue growth seen in the first half is expected to continue into the
second half, with the majority of the group performing at least in line with, or ahead of, expectations.
Europe is expected to continue to deliver steady underlying growth for the rest of the year and Asia Pacific should maintain its strong performance. However, the US will remain a problem for TNS.
"The group indicated at the time of the preliminary results in March that it could not be certain when the US custom business would return to growth. Although visibility is limited, due to the short-term nature of the business, forward-looking order book information now indicates that this is unlikely to happen in 2006," TNS said in a statement.
"As outlined above, action has been taken already to reduce operating costs significantly but the benefits of this action will not be fully felt until 2007. It is possible, therefore, that group operating margin before exceptional costs could decline," TNS said.
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