Aegis' case was initially thrown out of court last month after KR Media's legal team successfully challenged claims that its two chief executives, Eryck Rebbouh and Bruno Kemoun, both former Carat chief executives, had engaged in illegal client poaching.
Aegis appealed against the decision and the French Appeal Court today found KR's legal defence had "serious flaws", allowing Aegis to continue its battle.
It is good news for Aegis, which was originally ordered to pay fines of up to £9000 a day until documents seized in the raid were returned to KR Media. It is estimated Carat's legal bill would exceed £100,000.
Rebbouh and Kemoun launched KR Media a year ago in Paris, and six months later WPP Group bought a 20% share in the company, in a deal that would give KR Media access to the media giant's systems, research and group-buying clout.
It has been successful in poaching clients of Carat including LVMH and Bouygues Telecom.
The pair's departure in November 2003 rocked Carat and left it with a major hole. The two, who also sat on the Aegis board, had worked with the group for 18 years.
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