Since French group Havas Advertising pulled out of the deal, CIA-owning Tempus's share price has fallen well below WPP's 555p-a-share offer. The situation deteriorated further following the terrorist attacks in the US.
Following the attacks and the plunging world markets, WPP CEO Sir Martin Sorrell is reported to have been examining whether he could exercise the little used "material adverse change" clause to get him out of the deal.
However, a report by investment bank Credit Suisse First Boston has revealed that this clause can only apply to a specific company and not weakness in a sector or a market downturn.
According to the bank, the government panel that is overseeing the bid will not accept the material adverse change argument.
Shares in WPP climbed 5.6% in early afternoon trading in London to 553.5, while Tempus fell 1% to 490.
CSFB said that if WPP is forced to go ahead with the deal, overpaying by between £200m and £300m for Tempus would not be "catastrophic for a company of WPP's size".
If WPP does go ahead and buy Tempus, it has until October 22 to satisfy all requirements of takeover law.
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