The move comes as Cello's first half financial results are reported to be ahead of market expectations.
Cello is to acquire 50.1% of Oomph for around 拢300,000, comprising 拢150,000 in loan notes and 123,254 new Cello ordinary shares, valued at 122p.
Last week Cello bought advertising agency The Farm for an undisclosed sum.
The remaining 49.9% of Oomph remains in the hands of the founders, Stephen Priestnall and Rodger Williams. They have the option to sell their stake for a maximum amount of 拢1.5m, payable up to 75% in new ordinary shares.
Oomph's clients include Co-operative Financial Services and Cottswold Outdoor. Oomph already works closely with Cello's data analytics subsidiary Talking Numbers.
In a trading update today, Cello said its response and data division had performed well in the first six months of the year, "showing well above industry average organic growth in both revenues and profit".
It highlighted the "excellent performance" of its research division, which includes healthcare market research business Insight.
Trading at its brand strategy and consulting division was described as "satisfactory". The division includes TMI and Leith. Cello said last week that it plans to merge the London office of Leith with The Farm.
Mark Scott, chief executive of Cello, said: "The ability of Cello to incubate outstanding new businesses will stand us in good stead as we seek to continually innovate in the solutions we offer clients."
The group said its outlook for 2006 remains positive with all three divisions showing good revenue growth and forward visibility.
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