But Havas could raise its offer, receiving encouragement from the relationship between WPP's chief executive Sir Martin Sorrell and Tempus' founder and chief executive Chris Ingram.

BBC: Ad agencies target media buyers

But analyst believe Mr Ingram, who still owns 16% of the company, and other senior Tempus managers may have been mollified by tempting job offers from WPP.

BBC: Ad agencies target media buyers

The two do not see eye to eye, said analysts, after Sir Martin and WPP's 22% stake in Tempus was bought for about 200p per share from a disgruntled former executive, reportedly against the will of Mr Ingram.

BBC: Ad agencies target media buyers

Ed Grebeck, chief executive officer of Tempus Advisors and a veteran of the bond markets, said he thinks the markets are more concerned about the longer-term health of the U.S. economy, rather than the short-term fix of raising the debt ceiling.

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