The company, which is currently rebuilding its US-based business, reported a 3.5% rise in revenues to £497.4m.
Its UK revenues grew by 10.2% to £78.8m, making it the second-best performing region after the Asia Pacific, Latin America and Middle Eastern region, which was up 14.7% to £78.8m.
TNS said some of the improvement was attributable to acquisitions it completed in December 2006, and that it was now benefiting from an improved organisational structure.
Meanwhile, the group's North American revenues dropped 1.9% to £99.2m.
David Lowden, chief executive of TNS, said: "Effective implementation of our strategy has delivered a good performance in the first half of 2007. As the group continues to execute against strategy, TNS remains confident in its outlook for the year and expects to continue to achieve year-on-year improvement in underlying revenue growth."