WPP, the UK advertising agency, would be unable to cite the terrorist attacks in the US as a justification to withdraw its offer for Tempus, the UK media buying agency, according to senior sources close to the deal.

Bankers close to the deal said that any request by WPP and its advisers to withdraw its 555p (€8.85) offer for Tempus, under the 'material adverse change clause', would be blocked. It is understood that the Takeover Panel, which would be asked to rule on the issue, is unlikely to accept the argument that there has been a material change in Tempus' position since the attacks.