The chief executive of Imago Y&R, which is 25% owned by WPP's Young & Rubicam, in Harare has been named as the architect of the ruling Zanu-PF party's election advertising campaign.
The campaign, which has been marred by the murder of opposition activists, is being run by Sharon Mugabe, who is said to be a cousin of the African leader.
According to a report in the Sunday Times, she is believed to be behind an ad campaign that directs anger at former colonial rulers the British, portraying them as pith helmet-wearing, lazy imperialists.
One ad features a white man in his Pith helmet being carried in a hammock by African servants. The text reads: "The British came only to seize land, conquer and enjoy life on our land at our expense. It's now time for us to enjoy the gains of our independence."
It implies that voters will benefit if more whites are driven out of the country. Many white farmers have been murdered by Mugabe henchmen and more have been driven from their homes in recent years as Zanu-PF seizes their land.
WPP acquired the agency in 2000 and Sir Martin Sorrell, the WPP chief executive, has now ordered it be sold. A sale would mean offloading WPP's stake to Mugabe for a nominal sum.
Sharon Mugabe only became involved with WPP when she bought the majority stake in the agency in 2006 from its white owner. WPP said it had asked Sharon Mugabe if she was linked to the Zimbabwean president and she had told the company she was not.
However, the opposition party the Movement for Democratic Changes believes she is a cousin of the corrupt president who is facing a run off in a second presidential election after failing to win the first one.
Bernard Barnett, WPP's corporate vice-president EMEA, said: "This is a disgraceful regime and we want no connection between Y&R and it."
WPP is not the first British agency group to be caught up in Zimbawbe. In March, Bell Pottinger's public affairs arm held talks about lobbying on behalf of Zimbabwe.
However, agency boss Peter Bingle turned down the chance to work for the regime.
Bingle, chairman of Bell Pottinger Public Affairs, made the admission to the Commons public administration select committee.